I've noticed that I'm more likely to be nicer to people who have an avatar. The more real the avatar the more I feel compassion for the person I'm talking to. It doesn't have to be a picture of the person, just a picture of something I recognize as having basis in reality. Do you find the presence of an avatar makes you more sympathetic?
Yes, it does. Now bugger off! (I really don't know. I suspect it makes a difference for some people, as the perception of anonymity can make people behave poorly according to some studies I've read, but I don't think I'm discourteous to people who don't have a profile pic — at least no more so than to those with a profile pic.)