What's the role of altruism in Buddhism?

The world is currently in a really bad place therefore no amount of altruism can tangibly make the world a better place.

For example, I often give what i can to independent reporters who risk their lives in foreign countries (or report other things) but, in reality, that is a waste of time because so few people listen to their reporting.

Or recently I gave some donations to Beirut & Gaza but I trust the Gaza donation won't do much.

The role of altruism is to make your heart & hands open; so you are free from miserliness & hardheartedness.

For example, when a Devadatta enemy came trolling for donations for his friend on DW, I immediately gave a donation without a thought. Someone asked me so I gave.

Then when another Devadatta enemy criticized me, I gave another (small) donation in his name to save his soul from rebirth punishment with King Yama in Niraya Hell.

This is what altruism is. When reasonably asked, you give.

The only purpose is the development of your heart to be unselfish; without fear.

And what is the wealth of generosity? Here, a noble disciple dwells at home with a heart devoid of the stain of miserliness, freely generous, openhanded, delighting in relinquishment, devoted to charity, delighting in giving and sharing. This is called the wealth of generosity.

Idha, bhikkhave, ariyasāvako vigatamalamaccherena cetasā agāraṃ ajjhāvasati muttacāgo payatapāṇi vosaggarato yācayogo dānasaṃvibhāgarato.Idaṃ vuccati, bhikkhave, cāgadhanaṃ.

AN 5.47

How important is to buddhist to make the world a better place, not just by developing negative (as "absence of something", not as "bad") wholesome qualities, but by changing the general conditions of the world?

In terms of logical expression, the absence of something is actually a super-set that already includes positive forms. Ex: "one who is NOT an idiot" is a super-set of all sets of people from average intelligence, above-average, high, superior, to vastly superior intelligence. So the common application of negation in Buddhist text is actually a good thing, for it provides an umbrella term that covers the full spectrum of all practitioners from beginners, regulars, advanced, all the way to the fully enlightened, hence including all facets of training, from mere abstaining from doing harms, to actively engaging in positive wholesome conducts.

The Dhammapada teaches to leave miserliness and embrace giving and charity.

177. Truly, misers fare not to heavenly realms; nor, indeed, do fools praise generosity. But the wise man rejoices in giving, and by that alone does he become happy hereafter.

223. Overcome the angry by non-anger; overcome the wicked by goodness; overcome the miser by generosity; overcome the liar by truth.

Iti 26 (below) has a strong message to give and to share, even the last bite, the last mouthful, but of course, the purpose is to remove the stain of selfishness from the mind, in addition to helping others.

This was said by the Blessed One, said by the Arahant, so I have heard: "If beings knew, as I know, the results of giving & sharing, they would not eat without having given, nor would the stain of selfishness overcome their minds. Even if it were their last bite, their last mouthful, they would not eat without having shared, if there were someone to receive their gift. But because beings do not know, as I know, the results of giving & sharing, they eat without having given. The stain of selfishness overcomes their minds."

AN 3.57 (below) praises charity and giving even to animals, but does say that it is far better to give to a virtuous person rather than an unvirtuous person.

"I tell you, Vaccha, even if a person throws the rinsings of a bowl or a cup into a village pool or pond, thinking, 'May whatever animals live here feed on this,' that would be a source of merit, to say nothing of what is given to human beings. But I do say that what is given to a virtuous person is of great fruit, and not so much what is given to an unvirtuous person. And the virtuous person has abandoned five factors and is endowed with five.

Iti 100 (below) talks about different types of donations and states that the donation or gift of the Dhamma (teachings) is the best type of donation or gift:

"There are these two kinds of gifts: a gift of material things & a gift of the Dhamma. Of the two, this is supreme: a gift of the Dhamma.

"There are these two kinds of sharing: sharing of material things & sharing of the Dhamma. Of the two, this is supreme: sharing of the Dhamma.

"There are these two kinds of assistance: assistance with material things & assistance with the Dhamma. Of the two, this is supreme: help with the Dhamma.

"There are these two kinds of mass-donations: a mass-donation of material things & a mass-donation of the Dhamma. Of the two, this is supreme: a mass-donation of the Dhamma."

AN 8.33 (below) states 8 reasons for giving:

Bhikkhus, there are these eight grounds for giving. What eight? (1) One gives a gift from desire. (2) One gives a gift from hatred. (3) One gives a gift from delusion. (4) One gives a gift from fear. (5) One gives a gift, thinking: ‘Giving was practiced before by my father and forefathers; I should not abandon this ancient family custom.’ (6) One gives a gift, thinking: ‘Having given this gift, with the breakup of the body, after death, I will be reborn in a good destination, in a heavenly world.’ (7) One gives a gift, thinking: ‘When I am giving this gift my mind becomes placid, and elation and joy arise.’ (8) One gives a gift for the purpose of ornamenting the mind, equipping the mind. These are the eight grounds for giving.”

However, AN 7.52 (below) states that adorning the mind is the best reason for giving. From this answer, "adorning the mind" means making the mind more virtuous, similar to Iti 26 above.

“Sāriputta, someone who gives gifts, not for any other reason, but thinking, ‘This is an adornment and requisite for the mind’, when their body breaks up, after death, is reborn among the gods of Brahmā’s Host. When that deed, success, fame, and sovereignty is spent they are a non-returner; they do not return to this state of existence.

So, from the perspective of Buddhism:

• Not all reasons to give are equal. The reason to adorn the mind is the best reason, more so than trying to change the world and make it a better place.
• Not all gifts are equal. The gift of the Dhamma (teachings) is the best.
• Not all recipients are equal. Giving to a virtuous person is better than giving to an unvirtuous person. Giving to a human is better than giving to an animal.

If you really want to change the world with a very significant impact, you must be a wheel-turning monarch (DN 26).

But the Dhammapada states that stream entry is better than becoming a wheel-turning monarch:

178. Better than sole sovereignty over the earth, better than going to heaven, better even than lordship over all the worlds is the supramundane Fruition of Stream Entrance.

So, no matter how you look it, the main goal of altruism in Buddhism is always adorning the mind, which based on AN 11.1, leads to stream entry and then to permanent extinguishment of suffering.

Altruism is defined as the belief in or practice of disinterested and selfless concern for the well-being of others.

With respect to Buddhism, altruism is therefore:

AN4.95:1.4: one who practices to benefit others, but not themselves;

Quite significantly, Buddhism goes further:

AN4.95:3.2: The person who practices to benefit themselves, but not others, is better than both of those.

Importantly, those who practice to benefit themselves but not others are not practicing stinginess in the conventional sense. Rather, those who practice to benefit themselves but not others are in seclusion extinguishing defilements of self-involvement.

Ultimately, Buddhists ideally practice to benefit themselves and others:

AN4.95:3.3: But the person who practices to benefit both themselves and others is the foremost, best, chief, highest, and finest of the four.

When I first read this, I found it a startling departure from my preconception that altruism was the highest ideal.

A parallel consideration here is that altruism concerns itself with "good deeds". Here, too, the Buddha says quite simply:

AN4.233:1.3: There are dark deeds with dark results; bright deeds with bright results;

But the Buddha goes on to say more:

AN4.233:1.5: dark and bright deeds with dark and bright results; and neither dark nor bright deeds with neither dark nor bright results, which lead to the ending of deeds.

We're all familiar with the muddle of dark and bright. But what is the fourth goal?

AN4.233:5.1: And what are neither dark nor bright deeds with neither dark nor bright results, which lead to the ending of deeds? It’s the intention to give up dark deeds with dark results, bright deeds with bright results, and both dark and bright deeds with both dark and bright results.

That fourth goal leads to the end of suffering for all.

When it comes to Buddhism applied to social ethics, we must emphasize Peace, Health, and Harmonious co-existence (with other people and species) as the key goals to aim for, both tactically and strategically.

In effect you are asking whether one should focus on not creating the opposites of these three in one's own life vs. actively working out there in the world to cultivate them at the level of society at large.

I think the answer is obvious. The first is limited to self and the second is unlimited and more strategic. This difference in attitude has long been a point of contrast between Mahayana and other schools.

Of course one should be careful to avoid creating War, Diseases, and Conflict while unskillfully trying to promote Peace, Health, and Harmony. This is why Buddhism often insists on first healing oneself to a sufficient degree, before trying to help the others.

But in general I don't think there's a contradiction between active altruism and "negative altruism" as long as you define your goal correctly as Peace-Health-Harmony. The conflict only arises if you define altruism as helping people attain better quality of life or attain their desires - then it gets troublesome, because they may be at odd with the Buddhist goals.