Isn't it an in game rule that you cannot play as a true atheist because there weren't really any in the middle ages? You can play as a pagan and reject the organized religions of the game but it's assumed you would have loose superstitions of some kind because this is a prescientific society. Further you'd have to accept that people will have a reason to look down on you for following "peasant superstitions". If people can't separate their character's religious beliefs from their own then role playing games might not be for them. This goes back to criticism of DnD in the 1980s and it's no more valid now then it was then.
