> We have this idealized version of ethics and rationality that maps poorly onto reality. Yet everybody (especially on social media) talks as if this idealized version is the obvious natural state of all humans.

So i'm not sure how much of it is "natural" or "cultural", but as others have pointed out the vast majority of people are happy to cooperate and help one another... it's not an abstract ideal.

On the other hand, since we were kids starting at school, and across the media spectrum, we've been taught to crush others to move forward. That part is definitely not natural but cultural. If that's the "reality" you're talking about, we can do a great deal about it!