Well there is an Atheistic philosophy called Satanism that doesn't have anything to do with the biblical Satan, except as a metaphor.
http://en.wikipedia.org/wiki/LaVeyan_Satanism#Magic
It's a bunch of bullshit and bad philosophy, combined with theatrics. I think the reason that many people think Atheism has something to do with Satanism most is two-fold.
A. They don't really know that much about either one, and somebody else told them so.
B. They are stupid.
http://en.wikipedia.org/wiki/LaVeyan_Satanism#Magic
It's a bunch of bullshit and bad philosophy, combined with theatrics. I think the reason that many people think Atheism has something to do with Satanism most is two-fold.
A. They don't really know that much about either one, and somebody else told them so.
B. They are stupid.