Actually the fact you can't provide physical proof of your deity would probably have something to do with it, and I don't say that condescendingly. You can argue about the history or social aspects of a given religion and other things of that nature, but you can't really argue about the validity or "reality" of it. It'll almost always boil down to the importance of faith over physical evidence, and if someone truly believes in those things, they'll stick to them. I have no issue with what others believe, I just think it's silly to argue over.