There's probably a lot of reasons building up to this. I suspect that a lot of this comes from the constant reinforcement of equality as broad concept. The idea

There's probably a lot of reasons building up to this. I suspect that a lot of this comes from the constant reinforcement of equality as broad concept. The idea that all people should have equal opportunities seems to have been perverted by some into the idea that all people should be the same. Then there's the idea of america as "one nation" instead of a massive collection of communities. Throw in the american need to spread out, and you start to get this culture that is far more homogenous than in the patchwork of cultures of europe and africa. So with that backdrop, it seems the problem is people who think they're the same get shocked to find out they're not.