I've said it often here: the more I used to argue with liberal Democrats when I worked back in Beltway Land, the more theistic I used to get. Now, the more I argue with creationists, the more atheistic I get.
I'm pretty close to the edge these days. But, unlike my pre-teen self in Sunday School, I feel no need for stealth. If fervor for the Church of Atheism strikes me, I'll say so. But I still don't see how anyone can think they know something that has to be completely divorced from observable experience.
Faith either way, with this qualifier...
In the case of a believer, they might have observable inner experience which is nevertheless not replicable. But the at least have a data set of one. The quandry of the atheist is determining whether their lack of an inner experience implies a data set even that large.
That position is not necessary to be an atheist and I'm sure there aren't many who hold this extreme view. Most of them (including me) are as sure that gods do not exist as many non-atheists are convinced of the nonexistence of leprechauns, IPUs and the like.
There is a subtle philosophical distinction. The atheist says: "You -- Mr. Theist -- have no evidence, and until you do, there is nothing for me to consider."
The agnostic looks at the same data and says: "True, there's no evidence for theism, but what do I know? It might be true anyway."
So in this context, the agnostic looks at the absence of evidence and still holds open the likelihood that there may be a case to be made. The atheist doesn't exactly say there's no god (some do, but not as I'm defining it), just that there's no reason for him to even consider the possibility until some evidence turns up. As I said, it's a subtle difference.