Why are us humans so stubborn?

It's hard to understand why most of us are mean to one another and That's what upsets me about how far we've come as a society, we treat people differently for no logical reason at all and what exactly are people gaining from that, because it is not respect from their peers.

The only answer i can come up with as to why people do this is that they were raised to believe certain stuff about people and for others those beliefs have always been embedded in their mind and have never changed their views. Either way, we shouldn't judge anybody for whatever the reason. It's not ok and will never be.