After viewing a couple of heating online discussions recently I've come to a conclusion. The source of all flame wars is an inflated ego. It frequently happens that someone makes a comment or asks a question that someone else, in his "wisdom," sees as stupid. Instead of keeping his mouth shut because it isn't that important or taking the time to figure out a charitible way to call attention to the defect, he has to show his superiority by making a flip or terse or sarcastic comment. The other person's feelings are hurt (read, his ego is deflated), so he responds with some kind of insufficiently thought out comeback.
For me, the solution is to be aware when I feel that "feeling" and find something else to do for the time being. Wait until the wave of emotion finishes sweeping over me, and then pray and think about a response, or not.