Over the years I've participated in quite a number of "spirited debates", on a variety of topics (everything to motorcycle helmets to the identity of MacBeth's real author.) And, to be honest, I don't think I've ever changed anyone's mind. I think a lot of people could probably say the same thing. Why is this? Why is it, that no matter how authoritative and conclusive the evidence we present, those with differing opinions simply fail to be swayed? Answer: A psychological phenomenon called the Backfire Effect. Participating in online debates can be still be a rewarding experience. Many commenters are witty, funny, knowledgeable, and articulate. But participate in the interest of adding to your own knowledge. Because expecting to fundamentally change someone else's mind is an exercise in futility.