Human beings are instinctively tribal, and when we think in terms of “us” vs. “them” the temptation to dehumanize the other is hard to resist when the stakes are high.
You see this most often in war, but even in smaller things, the tendency pops up. I know plenty of people who instinctively cringe when they hear a certain accent, and of course, plenty of people assume evil of people on no basis other than skin color.
