The problem is that all creatures are hardwired to be suspicious and fearful of difference. The sad thing is that there is a good reason for it. That is to say, folks of a kind working together for a purpose is how things get done. The cost unfortunately for such positive gain is conflict, hate and war between dissimilar factions. In this bittersweet world that is just the way it is.
As I have written many times if you alternately placed red and blue armbands on folks entering a stadium, it would not be long before the folks in blue would find fault with the folks in red and vice versa. It is the competitive emotion that drives sporting events as well as war.