It costs nothing to be polite. I've always believed that how you conduct yourself is a reflection of your self-esteem. When you go out of your way to be nasty to people, it says a lot. Lack of control over your life maybe, so you attempt to exert power over other people to feel better? Who knows? Why take out your frustrations on strangers? If somebody does something dumb that I can't stand, I just leave. I don't feel the need to heckle them.
This post reminded me of something a late family member said about WoW's community once:
"So many toons, yet so little character."
It was so profound and simple. You have to be the change you want to see in the world, and I think that applies to virtual worlds too. Treat people as though the community is as friendly and warm as you wish it was.