Why do some people hate being individual from each ther?

What I'm saying is that some people belief in te fact that we should kill others just because there different and be prejudice just because there different. We start wars just because some people have different ideologyies and we should not fight because of it we should respect are differences. Anyhow we are all humans and we are all diffrent by culture and should not e fighting over this fact. But please tell me what you think about the fact that people are different. Thanks for reading and answering.