Is Buddhism a teaching of ethical neutrality

As in regard of the Dhamma, right view, good householder gains a broad overview here: How to address wrong view?

Only if not harming or breaking precepts, one leaves neutrality, while inwardly, of course, right view, not left view or wrong view, always domains for the Dhammica.

Loss of everything, beginning with relations, isn't that bad as to lose right view, metta.

AN 1.071-080: Kalyāṇamittādivaggo: Good companionship and others

The question here appears faulty. To suggest some rewording to generate an answer to the question:

In situations involving lies and/or violence, often Buddhism teaches (siding with truth) that lies and violence often beget lies and/or violence. For example, merely about speech, the Dhammapada says:

133. Speak not harshly to anyone, for those thus spoken to might retort. Indeed, angry speech hurts, and retaliation may overtake you.

Not exactly what you're looking for, though the Bodhisattva Never Disparaging story from chapter 20 of Lotus Sutra contains some similar elements. The story is popular where I live, but I haven't seen it around here much so I assume members of BSE might not all be familiar with it.

"At this time there was a bodhisattva monk named Never Disparaging. Now, Gainer of Great Authority, for what reason was he named Never Disparaging? This monk, whatever persons he happened to meet, whether monks, nuns, laymen, or laywomen, would bow in obeisance to all of them and speak words of praise, saying, ‘I have profound reverence for you, I would never dare treat you with disparagement or arrogance. Why? Because you will all practice the bodhisattva way and will then be able to attain buddhahood."

“This monk did not devote his time to reading or reciting the scriptures, but simply went about bowing to people. And if he happened to see any of the four kinds of believers far off in the distance, he would purposely go to where they were, bow to them, and speak words of praise, saying, ‘I would never dare disparage you, because you are all certain to attain buddhahood!’

“Among the four kinds of believers there were those who gave way to anger, their minds lacking in purity, and they spoke ill of him and cursed him, saying, ‘This ignorant monk—where does he come from, presuming to declare that he does not disparage us and bestowing on us a prediction that we will attain buddhahood? We have no use for such vain and irresponsible predictions!’

“Many years passed in this way, during which this monk was constantly subjected to curses and abuse. He did not give way to anger, however, but each time spoke the same words, ‘You are certain to attain buddhahood.’ When he spoke in this manner, some among the group would take sticks of wood or tiles and stones and beat and pelt him. But even as he ran away and took up his stance at a distance, he continued to call out in a loud voice, ‘I would never dare disparage you, for you are all certain to attain buddhahood!’ And because he always spoke these words, the overbearingly arrogant monks, nuns, laymen, and laywomen gave him the name Never Disparaging.

This particular Bodhisattva (later revealed to be a previous incarnation of Gautama)

• Spoke the truth but was perceived by others to be lying (which did nothing to hinder him).
• Was subjected to many extreme reactions, often violent (which also did not hinder him).
• Was always respectful to others and never stopped believing in the Buddha nature of all sentient beings.

Nichiren comments that, as the story is set in the age of set in the age of mappō, a lot of people, monks and lay alike, cannot discern what is or isn't authentic Dharma. Therefore those who say the absolute truth in the most direct and unobscured way is also the most authentic.

The Bodhisattva's way of dealing with extreme reactions is to have a healthy boundary - running away when necessary, but still comeback to enlighten beings when things are more cooled down. A form of non-violence that is not too naive or passive.

For my health issues, I recently worked with a healer who emphasizes a vegan diet.

[BTW he's also a staunch Buddhist, and no I've not been 100% successful as a vegan 🙃]

One day, while really enjoying my smoothie I had an epiphany:

Its not that veganism is not to eat this or that. But rather its a positive: to eat and enjoy and relish some wonderful things we neglect to remember/try.

I believe your question, like my vegan experience, suggests exploring a frame inversion from an implied negative to an actual positive.

_{I'm new here and its a bit strange that I am answering a moderator, especially to what certainly looks like a sincere question.}

It is somewhat a truism but still reasonably true to take as a starting point: The Eastern religions are wisdom-oriented, the Abrahamic are faith-and-value oriented.

Of course one can find as many exceptions to this as one likes. eg

How much better to get wisdom than gold, to get insight rather than silver!
Proverbs 16.16 from Bible

Still if we allow the stereotype a little room it becomes possible to consider that your question has a framing problem:

Is Ethics/ethicality a central Buddhist concern or is Buddhism closer to wondering… What is ethics? Why ethics? Which then inches towards: /What/Whither/Whence suffering? And thence pragmatic answers to that.

And if we would tarry a little with the wisdom angle it may help to connect with one of the greatest figures of wisdom in the western world: Socrates.

Socrates famously said: I do not know. Or more strongly: I know that I do not know. But there's something about Socrates' attitude that is not in any mere words: He seems to enjoy and relish his un-knowing!

My own teacher [who BTW has a comprehensive book on Buddhism] once said to me:

Its not just that Socrates said that I do not know. He said that since I do not know what death entails, I cannot possibly fear death!!!

And this shows why the earlier quoted biblical proverb is so true: True wisdom saves from the greatest of all fears.

It is from this view that (I feel) we need to hear Buddha.

To me the Buddha does not say:

I am the authority, I am the ultimate, believe and obey me.

He seems more to say:

Ive pondered reflected suffered and researched the problem of human suffering. These are my findings. I invite you to reflect on them and then research them in your own frame of reference.

In short Buddhism is not a weak negative toward ethics but a strong positive towards wisdom.

Comes to the reason of this post

You have — I assume recently — assumed a name for yourself out here. That name conveys a strong view, an opinion, a conclusion on a matter that seems of great importance.

Does that conclusion leave room for a question?

Try this thought experiment. Lets assume some figure such as say the Buddha who you regard as unequivocally, vastly wiser than you were here with us today. Would he have agreed with you? Are you sure?

Let me end with again a quote from my teacher from his book on the Bhagavad Gita

The eastern religions are consciousness oriented;
the middle eastern religions are conscience oriented

Today we are all neither eastern nor western, or both eastern and western.

We all need to practice the good Samaritan, turning other cheek, forgiveness in the face of provocation — the conscience-angle

But also, we need to put aside all this, to put aside all relationing and take to our meditation seats — the consciousness angle.

We simply do not have the time for This? OR That?
It must be This AND That!

Even (and especially when!!) the bombs fall!

The story of the Buddha stopping his relatives, the Sakyans and Koliyans, from getting into a war over water rights of the Rohini river, comes from the traditional commentary to Dhammapada 197 - 199.

The Buddha uttered Verse (197) to (199) of this book, in the Sakyan country, with reference to his relatives who were quarrelling over the use of the water from the Rohini river.

Kapilavatthu the town of the Sakyans and Koliya the town of the Kolyans were situated on either side of the Rohini river. The cultivators of both towns worked the fields watered by the Rohini river. One year, they did not have enough rain and finding that the paddy and other crops were beginning to shrivel up, cultivators on both sides wanted to divert the water from the Rohini river to their own fields. Those living in Koliya said that there was not enough water in the river for both sides, and that if only they could channel the water just once more to their fields that would be enough for the paddy to mature and ripen. On the other hand, people from Kapilavatthu argued that, in that case, they would be denied the use of the water and their crops would surely fail, and they would be compelled to buy from other people. They said that they were not prepared to go carrying their money and valuables to the opposite bank of the river in exchange for food.

Both sides wanted the water for their own use only and there was much ill will between them due to abusive language and accusations on both sides. The quarrel that started between the cultivators came to the ears of the ministers concerned, and they reported the matter to their respective rulers, and both sides prepared to go to war.

The Buddha, surveying the world with his supernormal powers, saw his relatives on both sides of the river coming out to meet in battle and he decided to stop them. All alone, he went to them by going through the sky, and stopped immediately above the middle of the river. His relatives seeing him, powerfully and yet peacefully sitting above them in the sky, hid aside all their weapons and paid obeisance to the Buddha. Then, the Buddha said to them, "For the sake of some water, which is of little value, you should not destroy your lives which are of so much value and priceless. Why have you taken this stupid action? If I had not stopped you today, your blood would have been flowing like a river by now. You live hating your enemies, but I have none to hate; you are ailing with moral defilements, but I am free from them; you are striving to have sensual pleasures, but I do not strive for them."

Then the Buddha spoke in verse as follows:

Verse 197: Indeed we live very happily, not hating anyone among those who hate; among men who hate we live without hating anyone.

Verse 198: Indeed we live very happily, in good health among the ailing; among men who are ailing we live in good health.

Verse 199: Indeed we live very happily, not striving (for sensual pleasures) among these who strive (for them); among those who strive (for them) we live without striving.

At the end of the discourse many people attained Sotapatti Fruition.

Dhammapada 197 - 199

On the other hand, monks are not allowed to participate in political activities which are divisive in nature.

Political activities often include divisive speeches to break people apart, and speeches where political opponents are belittled.

Political activities may or may not include false speech, transfer of money, possible bribery or deception, relaying of messages or running of errands for other people, making forecasts for political victories or failures, scheming, persuading, hinting and belittling.

"And how is a monk consummate in virtue? ....

"Abandoning false speech, he abstains from false speech. He speaks the truth, holds to the truth, is firm, reliable, no deceiver of the world. This, too, is part of his virtue.

"Abandoning divisive speech he abstains from divisive speech. What he has heard here he does not tell there to break those people apart from these people here. What he has heard there he does not tell here to break these people apart from those people there. Thus reconciling those who have broken apart or cementing those who are united, he loves concord, delights in concord, enjoys concord, speaks things that create concord. This, too, is part of his virtue.

"He abstains from accepting gold and money.

"He abstains from running messages... from buying and selling... from dealing with false scales, false metals, and false measures... from bribery, deception, and fraud.

"He abstains from mutilating, executing, imprisoning, highway robbery, plunder, and violence.

"Whereas some brahmans and contemplatives, living off food given in faith, are addicted to talking about lowly topics such as these — talking about kings, robbers, ministers of state; armies, alarms, and battles; food and drink; clothing, furniture, garlands, and scents; relatives; vehicles; villages, towns, cities, the countryside; women and heroes; the gossip of the street and the well; tales of the dead; tales of diversity [philosophical discussions of the past and future], the creation of the world and of the sea, and talk of whether things exist or not — he abstains from talking about lowly topics such as these. This, too, is part of his virtue.

"Whereas some brahmans and contemplatives, living off food given in faith, are addicted to running messages and errands for people such as these — kings, ministers of state, noble warriors, brahmans, householders, or youths [who say], 'Go here, go there, take this there, fetch that here' — he abstains from running messages and errands for people such as these. This, too, is part of his virtue.

"Whereas some brahmans and contemplatives, living off food given in faith, engage in scheming, persuading, hinting, belittling, and pursuing gain with gain, he abstains from forms of scheming and persuading [improper ways of trying to gain material support from donors] such as these. This, too, is part of his virtue.

"Whereas some contemplatives & brahmans, living off food given in faith, maintain themselves by wrong livelihood, by such "animal" arts as: reading marks on the limbs [e.g., palmistry]; reading omens and signs; interpreting celestial events [falling stars, comets]; interpreting dreams; ... ; making predictions for state officials; .....; casting horoscopes — he abstains from wrong livelihood, from "animal" arts such as these.

"Whereas some contemplatives & brahmans, living off food given in faith, maintain themselves by wrong livelihood, by such "animal" arts as [forecasting]: the rulers will march forth; the rulers will not march forth; our rulers will attack, and their rulers will retreat; their rulers will attack, and our rulers will retreat; there will be triumph for our rulers and defeat for their rulers; there will be triumph for their rulers and defeat for our rulers; thus there will be triumph this one, defeat for that one — he abstains from wrong livelihood, from "animal" arts such as these.

"Whereas some contemplatives & brahmans, living off food given in faith, maintain themselves by wrong livelihood, by such "animal" arts as [forecasting]: there will be abundant rain; there will be a drought; there will be plenty; there will be famine; there will be rest and security; there will be danger; there will be disease; there will be freedom from disease; or they earn their living by accounting, counting, calculation, composing poetry, or teaching hedonistic arts and doctrines [lokāyata] — he abstains from wrong livelihood, from "animal" arts such as these.

Samannaphala Sutta (DN2)

So, in conclusion, truth, non-violence, unity and peace is good. Lies, violence and divisiveness is bad. Speaking the truth and calling for peace, unity and non-violence is the right way in Buddhism.

I don't know how helpful this will be in your situation but I'll make it short:

IF you know the truth and somebody lies it is right to call it out. If you witness violence it is right to stop it if you can without being violent yourself (main options are: help the victim get away or restrain the aggressor and then get away). But the reason might suprise you.

You do it for the lier and the attacker not for the lied to and attacked. It is unbeneficial to lie or be violent so if you can you should prevent people from lying and attacking for their own sake.

should a Buddhist defend truth or is it preferred to remain uninvolved

Maybe it depends, on the topic perhaps?

When the topic is Dhamma there is for example MN 22:

Then those monks, desiring to pry the monk Arittha Formerly-of-the-Vulture-Killers away from that pernicious viewpoint, quizzed him back and forth and rebuked him ...

So when the monks were unable to pry the monk Arittha Formerly-of-the-Vulture-Killers away from that pernicious viewpoint, they went to the Blessed One ...

I'm not certain they did right; but then the Blessed One himself called, and rebuked, and corrected him.

Although, that's within the context of a pre-existing relationship: i.e. where the Buddha is formally the monk's teacher.

Outside of that relationship maybe what you do is "offer" the truth (especially but perhaps not only when asked), rather than being bossy about it. The Buddha himself started his mission only for "those with ears" in MN 26:

Then, having understood Brahma's invitation, out of compassion for beings, I surveyed the world with the eye of an Awakened One. As I did so, I saw beings with little dust in their eyes and those with much, [...] those with keen faculties and those with dull, those with good attributes and those with bad, those easy to teach and those hard, some of them seeing disgrace & danger in the other world.

"Having seen this, I answered Brahma Sahampati in verse:

'Open are the doors to the Deathless
to those with ears.
Let them show their conviction.

On other types of topic, "the truth" tends to be like an elephant (i.e. people's perception of it is subjective and partial):

• "He started!" -- "No, he started it!"
• "I am wronged!" -- "But what about [etc.]"

... which according to the Dhammapada might be "endless" if you're not careful, and which may call for a certain type of "neutrality".

Regardless, I think that Buddhism teaches that at least some things are an "absolute truth", and not only relative, for example (quoting from Getting the Message):

The early texts report that a group of wanderers, in a discussion with one of the Buddha's lay disciples, once accused the Buddha of not taking a position on any issue, and the disciple replied that they were mistaken. There was one issue on which the Buddha's position was very clear: what kind of behavior is skillful, and what kind of behavior is not. When the disciple later reported the conversation to the Buddha, the Buddha approved of what he had said. The distinction between skillful and unskillful behavior lies at the basis of everything the Buddha taught.

In making this distinction, the Buddha drew some very sharp lines:

"What is unskillful? Taking life is unskillful, taking what is not given... sexual misconduct... lying... abusive speech... divisive tale-bearing... idle chatter is unskillful. Covetousness... ill will... wrong views are unskillful. These things are called unskillful...

"And what is skillful? Abstaining from taking life is skillful, abstaining from taking what is not given... from sexual misconduct... from lying... from abusive speech... from divisive tale-bearing... abstaining from idle chatter is skillful. Lack of covetousness... lack of ill will... right views are skillful. These things are called skillful."

— MN 9

Killing is never skillful. Stealing, lying, and everything else in the first list are never skillful. When asked if there was anything whose killing he approved of, the Buddha answered that there was only one thing: anger. In no recorded instance did he approve of killing any living being at all. When one of his monks went to an executioner and told the man to kill his victims compassionately, with one blow, rather than torturing them, the Buddha expelled the monk from the Sangha, on the grounds that even the recommendation to kill compassionately is still a recommendation to kill — something he would never condone. If a monk was physically attacked, the Buddha allowed him to strike back in self-defense, but never with the intention to kill.

On the subject of "the elephant" I try to keep in mind:

• Ud 6.4 (a war of words, "wounding with weapons of the mouth", arguments that generate more heat than light)
• The definitions of "conceit" given by Ven. Yuttadhammo and by Wikipedia, given that canonically conceit is a major cause of dispute
• A "young Quaker" telling me once, "I'll discuss anything with anyone; but as soon it turns into an argument then I [...] walk away"

And I should possibly reference Right Speech also.

If someone violently attacks someone else, does Buddhism teach pacifying the attacker and defending the victim, or does it teach staying out?

As I remember it, when someone was going to make war on the Sakyans, the Buddha tried to dissuade them (verbally) -- but when that failed he (of course) didn't participate in the war.

If you want to know about "violence" specifically, I think it's not completely unheard of -- the Vinaya says something like, that if a monk is (physically) seized then "they may, desiring freedom, strike a blow".

My personal experience (if that's on-topic) of intervening in a fight is not extensive, but in an immediate emergency my recollection is of acting without a lot of introspection: see or hear a commotion; perceive who's involved; feel it would be better for it to be more peaceful; move to act on that intention. And you do it because you're there and you can. And it doesn't feel personal, it feels (rightly or wrongly) like a case of "anybody would have done the same, or should have if they could", or (for better or worse) "instinctive" (maybe like this quote, "I would have no hesitation") -- like saving somebody else from danger, from drowning. There's one instance I recall vividly, I don't regret (feel remorse about) doing it. I'm not proud of how skilfully I did it -- I grabbed the attacker's hair from behind and dragged him off -- but other people were already standing around shouting, apparently I computed that "direct action" was the solution then, it was effective and mostly harmless.

As for "defending the victim" perhaps that's always an option too, especially for a lay-person. I mean it's traditional for concientious objectors now to go to war as "stretcher-bearers" i.e. to help the victims. It must be a bit different for monks -- they can't give money to the Red Cross, obviously. I suppose the Vinaya even technically forbids their giving medical assistance (but possibly "first aid" would be another case of "do it if you have to, confess it afterwards").

One more thing on the subject of "lies and violence", one of the first things they had me memorize from school was La Fontaine's "The Wolf and the Lamb". With that, and with what I know of causus belli historically, it's entirely unsurprising to me, old news, that violence is associated with lies -- see also, "ultima ratio regum".

Given that, and given how it's possible to become swept up in unproductive argument -- if "the Wolf" will not take "no" for an answer, and if you have yourself renounced the "last argument of kings" -- then sometimes "the only winning move is not to play". Or to do it elsewhere -- "right speech" being "spoken at the right time".

For a global perspective, we should probably all review DN16. The wisdom that follows this introduction is worth reading in its entirety. It is subtle and not easily summarized. The problem, however, is summarized succinctly:

DN16:1.3.5: Master Gotama, King Ajātasattu wants to invade the Vajjis.
DN16:1.3.6: He has declared:
DN16:1.3.7: ‘I shall wipe out these Vajjis, so mighty and powerful! I shall destroy them, and lay ruin and devastation upon them!’”

For actions, let ethics guide us:

MN8:12.2: ‘Others will be cruel, but here we will not be cruel.’
MN8:12.3: ‘Others will kill living creatures, but here we will not kill living creatures.’
MN8:12.4: ‘Others will steal, but here we will not steal.’
MN8:12.5: ‘Others will be unchaste, but here we will not be unchaste.’
MN8:12.6: ‘Others will lie, but here we will not lie.’
MN8:12.7: ‘Others will speak divisively, but here we will not speak divisively.’
MN8:12.8: ‘Others will speak harshly, but here we will not speak harshly.’
MN8:12.9: ‘Others will talk nonsense, but here we will not talk nonsense.’
MN8:12.10: ‘Others will be covetous, but here we will not be covetous.’
MN8:12.11: ‘Others will have ill will, but here we will not have ill will.’
MN8:12.12: ‘Others will have wrong view, but here we will have right view.’
MN8:12.13: ‘Others will have wrong thought, but here we will have right thought.’
MN8:12.14: ‘Others will have wrong speech, but here we will have right speech.’
MN8:12.15: ‘Others will have wrong action, but here we will have right action.’
MN8:12.16: ‘Others will have wrong livelihood, but here we will have right livelihood.’
MN8:12.17: ‘Others will have wrong effort, but here we will have right effort.’
MN8:12.18: ‘Others will have wrong mindfulness, but here we will have right mindfulness.’
MN8:12.19: ‘Others will have wrong immersion, but here we will have right immersion.’
MN8:12.20: ‘Others will have wrong knowledge, but here we will have right knowledge.’
MN8:12.21: ‘Others will have wrong freedom, but here we will have right freedom.’
...

And if anger arises, let us all remember what the Buddha said:

SN1.71:2.3: What’s the one thing, Gotama,
SN1.71:2.4: whose killing you approve?”
SN1.71:3.1: “When anger’s incinerated you sleep at ease.
SN1.71:3.2: When anger’s incinerated there is no sorrow.
SN1.71:3.3: O deity, anger has a poisoned root
SN1.71:3.4: and a honey tip.
SN1.71:3.5: The noble ones praise its killing,
SN1.71:3.6: for when it’s incinerated there is no sorrow.”