why are people so mean?

I keep seeing people be mean to others even if it's just a small thing its weird like why are you so mean? I don't understand. Why have humans become so hateful and evil? I get sometimes arguments happen and sometimes its valid or whatever, but it just confuses how people can be so mean (without a VALID reason) I mean I've made mistakes and said certain things but it's just confusing to me. Why say things that don't even have to be said? Why not just be nice? Why do people use others? I have so many unanswered questions but it's not like anyone could give me a true answer. I don't even feel bad for others. I don't have that emotion towards them but I'm aware of what reality is and how others actually have feelings. I'm realistic. I could say I don't care for anyone because I don't really, but I do? my actions show I do but my actual feelings have nothing. I wish this world wasn't so fucking stubborn.