Excellent article. I think the problem goes back to a deep tribal instinct shared with our simian cousins (chimps, gorillas, etc.)--a fierce loyalty to "us" and corresponding fear and loathing of "them," however configured. The basis of the distinction between "us" and "them" is entirely arbitrary.

Here in (lily-white) Oregon where I live, for example, even college football teams become a basis for tribal loyalty. Here in Salem, just north of Corvallis, most people I meet are proudly "Beavers" meaning they have a degree from and/or are loyal fans of Oregon State U, whose chief rivals are the U. of Oregon "Ducks."

And although I have zero interest in college sports of any sort, if I tell folks that my degree is from the U. or O,, they will often say idiotic things like "Oh, so you are a Duck, eh? This is Beaver country..." This is a trivial example of our general tendency toward tribal loyalty and "othering" of the adjacent tribe. Racism is just a cultural tradition, deeply rooted in our history, of the same exact nonsense.