Is it true that atheism has killed more people then organized religion?...

[Entropist]

Atheism per se is not an ideology, but it makes a whole host of various ideologies possible. A secular humanist, an objectivist, and a nihilist may all be atheists of course, but the conclusions they reach (partly because they are atheists) are considerably different. Atheism by itself is not an ideology, but it usually leads to ideologies that could not be held by a theist.

Just because someone tells me they are an atheist (or a plain "theist"), they haven't told me very much about themselves at all.