Because they have to! This world is full of segregation! Religions, races, colors, wealth,.... Even if you got nothing. There is still DNA and fingerprint. Now your question has to be, how can we live peacefully with all these diversity? To make all people rational and liberal. Which is again impossible. Then how? Law and order. Is that possible? It depends but still cannot cure the cancer. So what? I don't know but Do what you gotta do! A neat and tidy world doesn't worth the cost man.