If they kept to themselves, then we would not ask for proof. But they don't, they knock on our doors, they protest the funerals of gay kids who commit suicide, they legislate to take away or deny the rights of people they dislike. They demand we believe as they do, they threaten us with eternal damnation if we don't. So we ask them, which god should we believe in? Buddha? Yahweh? Zeus? How do we know which one? Which version of the bible should we accept? We ask for proof, a reason go believe beyond 'I say so'.