I agree with your first paragraph, but I really, really have to ask you: don't you consider the threat of being burned for all eternity, postulated by Jesus himself as a punishment for not believing not enough motivation?
Atheism is not a thing, it is not a religion nor a political position; it is not a cult where everybody acts the same, thus you cannot "act like an atheist". There are no actions you are required to perform in order to be considered an atheist. You can even go to church every sunday, as many atheists do, and still be an atheist.