why do we hate on eachother all the time?

This is a serious question. I've read and heard countless instances of greek students hating on other greek students/organizations.

---For those of you who do not care for other greek students/organizations; could you tell me of some the instances/examples of what made you feel negatively towards certain organizations?---

I ask this because it seems anyone outside of greek life in today's society has negative feelings towards greek life. It would be nice to have the fraternities/sororities support their fellow greeks, instead of add to the criticism and hate we already get from society outside greek life. But that is kind of a pipe dream, so i'd like to know why we feel the way we feel towards each other.