There's diversity, where you have a lot of different types of people, and then there's places with a high concentration of a minority group

The first one makes people less bigoted, because you can't avoid dealing with people when they're everywhere. Your not going to last long in NYC if you don't want your food touched by them. Either you deal with it and get used to it, or you'll find it hard to eat

The second one doesn't force those normal human interactions. Instead, you have exposure. You see them around, but don't have to treat them like people. You might not interact at all.

So every time you see them, it reinforces the racism

You see it all over the American South, people around the black communities aren't less racist, they're giga-racist