Taking Vinaya as a measure of the weight of kamma?

Is such an idea legitimately or just another cherry-picking around to justify personal incapacities and giving favors?

Perhaps it's because the suttas and/or the precepts say e.g. "don't kill" but don't have as much detail as the Vinaya.

For example, if someone asks, "What if I cause someone to die by accident? What if I dig a pit and someone falls into it?", that's maybe not a question which is answered explicitly in the suttas or precepts -- but is a question that's considered in detail in the Vinaya.

So I suppose some people would prefer to rely on what they know of the Vinaya, instead of rely on their own interpretation of the suttas or precepts.

You might want people to rely on their own experience too (not just theoretical doctrine). But I suppose most people have little or no personal experience of digging pits and seeing other people die in them, so an answer based on theory might seem like all that's available.

It's not just "killing" -- I think the Vinaya details the necessary components of other offences (e.g. lying), which look like lay precepts too (e.g. the fourth precept), including ...

• Intent to deceive
• Effort to produce the deception

... which isn't detailed in the suttas (though you might justify it from the suttas). That's a topic which probably affects everyone (more than pit-digging does).

People do ask that kind of question -- see e.g. Trolley problem and its variants in Buddhist ethics (whether they should ask is another matter). Here was your answer to that, by the way:

It may lighten or make certain speculations irrelevant to be clear that one does not have any inherent obligation to "help" or "save", but this it self, the notion, is in fact an "obligation" out of unskillful gained debt, independency.

When I read it I assumed that Suminda's answer was based on the Vinaya (because its content is so similar). Reading its references now, though, I see it's based on a Tharavada text called the Atthasālinī, a commentary by Buddhaghosa on the Dhammasangani -- which ties somehow to what you said in the OP about Abhidhamma. I don't know from where or how Buddhaghosa derived those doctrinal details.

The "precise" definitions sometimes have behavioural consequences -- e.g. (rightly or wrongly) some people don't classify copyright as stealing, because making a copy doesn't deprive the owner of the original thing and/or other reasons (not that I want to debate that again here).

Incidentally I think you sometimes use "killing" and "stealing" metaphorically, which is hard to converse with -- "When will you stop beating your wife?" is an example of a so-called loaded question (actually I find a lot of your language is "loaded" in other ways, e.g. your saying "draw excuses" in the this OP above instead of "give reason" or "explain" has me thinking that you condemn that practice, and assume that you know better -- I guess the "law of nature" which you refer to later is "dhamma").

One more thing, I find that suttas don't explain karma in every detail. Perhaps I see in general what karma is, and perhaps what it isn't -- but I think that "the precise working out of karma" is one of the Buddha's supernatural powers -- I'm not sure I could answer any question about the "weight" of karma, though people try to compare different weights (see e.g. ruben's answer), with justification from the suttas.

You must be dissatisfied with my quote (in this answer) of killing humans being a parajika offense for monks vs. killing animals which is only a pacittiya offense. A parajika offense is met with immediate and irreversible dismissal from the monastic order. A pacittiya offense is met with confession, usually with the intention to not repeat it.

Firstly, let's get this right:

• Killing is against the first of the five precepts
• Business in meat is against Right Livelihood.
• Keeping the five precepts is one of the criteria for stream entry according to AN 10.92.

However, does this mean killing any living creature has the same consequence or same effects? Does killing a mosquito bear the same consequence as killing an arahant?

The answer is NO.

According to AN 6.87, there is actually a list of people a person could kill or injure, and such a person will never be able to have the right mental state or moral capacity to learn the Dhamma:

"Endowed with these six qualities, a person is incapable of alighting on the lawfulness, the rightness of skillful mental qualities even when listening to the true Dhamma. Which six?

"He has killed his mother; he has killed his father; he has killed an arahant; he has, with corrupt intent, caused the blood of a Tathagata to flow; he has caused a split in the Sangha; or he is a person of dull discernment, slow & dull-witted.

"Endowed with these six qualities, a person is capable of alighting on the lawfulness, the rightness of skillful mental qualities even while listening to the true Dhamma. Which six?

"He has not killed his mother; he has not killed his father; he has not killed an arahant; he has not, with corrupt intent, caused the blood of a Tathagata to flow; he has not caused a split in the Sangha; and he is a discerning person, not slow or dull-witted.

According to MN 86, Angulimala killed many human beings, but he could still change and become an arahant. So, probably, he did not commit the transgressions above (killing father, killing mother, killing arahant, injuring Buddha):

And at that time in King Pasenadi's realm there was a bandit named Angulimala: brutal, bloody-handed, devoted to killing & slaying, showing no mercy to living beings. He turned villages into non-villages, towns into non-towns, settled countryside into unsettled countryside. Having repeatedly killed human beings, he wore a garland (mala) made of fingers (anguli).

(After the Buddha transformed Angulimala)

Then Ven. Angulimala, dwelling alone, secluded, heedful, ardent, & resolute, in no long time reached & remained in the supreme goal of the holy life for which clansmen rightly go forth from home into homelessness, knowing & realizing it for himself in the here & now. He knew: "Birth is ended, the holy life fulfilled, the task done. There is nothing further for the sake of this world." And thus Ven. Angulimala became another one of the arahants.

On the other hand, according to DN 2, King Ajatasattu was unable to effectively learn the Dhamma because he had arranged to kill his father in order to become king:

So King Ajatasattu, delighting and rejoicing in the Blessed One's words, rose from his seat, bowed down to him, and — after circumambulating him — left. Not long after King Ajatasattu had left, the Blessed One addressed the monks: "The king is wounded, monks. The king is incapacitated. Had he not killed his father — that righteous man, that righteous king — the dustless, stainless Dhamma eye would have arisen to him as he sat in this very seat."