> People killing people is one of the better-documented aspects of human history. If it's really a commonly-held idea, it's a delusional one.

Lots of things are well documented. Famine is too, but it has a big negative impact.

Humans are social creatures that live exclusively in groups; they cannot survive alone psychologically or, usually, physically. Groups are effective when they are at peace; evolutionary psychology, at least, supports not killing each other.

A universal aspect of every human culture is a taboo against killing.