[Dirlewanger]

There's no doubt it's in our DNA. Forming groups with likeminded people is what kept our species alive for hundreds of thousands of years. And it's only been in the past ~150 years that we as a civilization have started to seriously care about the wellbeing of others unlike themselves. We've undoubtedly come a far way, but that's not to say we don't have much further to go. Fighting with our innate tribalistic tendencies is hard.