People have everything within them: we contain multitudes. But we also become what we do, and what we surround ourselves with.
Setting aside 4chan, which I don't know well, look at newspaper comments. People positively compete to be giant assholes. They practice being mean. I think there's a big difference between people having the potential for meanness within them and indulging that in a way that magnifies and sharpens it.
There are definitely contexts where people will talk honestly about the assholish thoughts and feelings we all have. E.g., I might tell a friend, "Man, I know that Bob means well, but I really can't stand him some times." That's honesty.
But for me to go and tell Bob, "Leave me alone you half-wit inbred nose-picker," that goes beyond honest to mean because I'm acting with clear disregard for hurting other people. And if I create a context where it's ok for people to be mean like that, I think it really is creating more meanness.