atheism can come in two basic forms, one of which is like the polar opposite of belief, never being taught about gods/deities. Without the concept of deity in your head, you either invent one, or never believe in one in the first place. This makes you an atheist, but one who is thoughtless about it, who simply can't think about it. So you have to be ignorant. This type of atheist is theoretical, most societies on Earth developed god beliefs of one sort or another.
The most common type of atheist today, at least in western societies are skeptical-atheists, who came to their non-belief through skepticism. The thing is, that skepticism, through critical thinking exercises, has to be taught, or, if it is an innate trait, reinforced, because it can be and has been abandoned by many people. I sometimes struggle to understand my own source for skepticism. I was raised nominally Catholic, however, my parents emphasized that I should examine and learn things on my own. Never take things at face value, and to argue things out with others, used to debate my mother all the time about all sorts of topics.
The thing is that these skills in critical thinking I was honing, I applied them to my entire life except to my religious beliefs, still believed in a god, even, at one point, attempted to resolve the my moral dissonance(problem of evil) with the biblical god by attempting polytheism through Wicca. This lasted quite a while, but eventually my effort at maintaining the mental blocks necessary to not apply skepticism to my religious beliefs fell apart, and so those beliefs also fell apart once critically examined. What's interesting is that I think I spent more mental energy trying to maintain those beliefs than I ever did applying critical thinking, introspection and skepticism to them. The question I have is did I have a choice here?
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