The fact that we have theoretical concepts of equivalence among people doesn't mean that they are easy to realize. We often fail to implement what we can imagine . Does that mean we ought to stop trying?

A longer and broader scope of history may also be less pessimistic. This cherry-picks the worst we can offer. It's easy to find these examples because humans are biased towards negativity by default. But tens of thousands of years of significantly cooperative culture in place, among aboriginal/indigenous humans in various parts of the world, is not a trivial example. Read "Dark Emu" by Bruce Pascoe, for example. We're only starting to acknowledge significantly egalitarian and peaceful cultures. Problem is, they tend to get overrun by violent autocratic cultures, whose autocrats then 'adjust' recorded history to make themselves look good.

A thought experiment to ponder is: how might a fundamentally peaceful egalitarian culture exist that would also be capable of defending itself against a violent dictatorial culture?