People are only mean when they're threatened, and that's what our culture does. That's what our economy does.
If humanity was still in the feral state, we wouldn't have any need for these huge conurbations that we have now, that have turned us into a different bunch all together. In the feral state we would be much more secure, much more familiar with each other, much more mentally well-balanced.
It's very clearly stated in the film: You make your own choices, and what you're always fighting is ego.

