Not only is religion intolerant of non believers, but especially of other religions. In fact, several main religions, if not all, claim martyrdom if you kill a person who is not in line with your path. Either believe what I believe, or I’ll kill you.
From hanging out with several friends to attending several churches, you really start to understand that every individual has a different interpretation of their own god and typically understand your own religious doctrine with your very own interpretation. I suppose one can say that there are many religions as there are religious people in the world.
This sort of ignorance usually tends to create friction among people. Friction that otherwise without religion, would either not exist, or another reason would have been found.