Why does it scare some people so much that one day everyone may be mixed?

Because separation makes it easier to have different cles. I thought about this for a while and I've seen that its no secret that many minorities are on the lower end of the spectrum (economically) unfortunately....but I think mixed is beautiful!! Plus some people might not want to inherit certain "sicknesses" that some races tend to have.....maybe like skin cancer in white people (its more common among them) just to use as an example, it was the first one that popped into my mind.....idk. There is really no harm in the world being mixed, its people's FEAR. Fear of losing their culture? Fear of something different? Fear of maybe not being a superior race or non superior race? Change tends to scare people for some odd reason.