I believe a lot of people who claim to be atheists are agnostic, as I am. Basically meaning I don't have proof against the existence of any religion's gods but I also have no definitive proof of their existence and therefore can't bring myself to believe in them. A lot of atheists are also more about disliking what the religion stands for or the people within it and disrespecting their religion by saying it's all fake. No one can prove anything one way or another.