When science and religion are compatable.

[Silent3]

48. While atheism is quite often a consequence...

...of a scientific world view, atheism itself is just a lack of belief in god, full stop.

You can arrive at atheism via multiple paths, and don't necessarily have to leave behind irrational or superstitious thinking. I suspect that some atheists are atheists for purely emotional reasons -- perhaps rebellion against strict religious parents, perhaps bad things have happened in their lives that make them leaps to a bitterness-fueled conclusion that no god can exist if these terrible things can happen, etc.

That said, all the atheists I personally know are the skeptically and scientifically-minded sort, and to the extent that there's an "atheist movement", skepticism and science are central to that movement.