Why do people self-segregate by race?

[Smid]

Almighty God created the races white, black, yellow, malay and red, and he placed them on separate continents. And, but for the interference with his arrangement, there would be no cause for such marriage. The fact that he separated the races shows that he did not intend for the races to mix.

Actually, this is totally contrary to what the Bible says. All the races are descended from Noah, his sons and their wives.