People who follow them may be stupid. May being the key word. Yes, I see that I am drawing a connection between stupidity and believing in a religion - it's an insult I suppose, but not entirely untrue based on my definition of stupid.
What do you call someone who believes in something that doesn't exist? Ignorant? Naive? Stupid? Crazy? What if that person - when confronted with overwhleming evidence running counter to their belief refuses to acknowledge the fact that their belief is not based on any form of measuarable proof (or fact)?