I think you've identified part of the problem with your assumptions, in that being an atheist doesn't define people, whereas to a great extent, theists are defined by their religious beliefs. The two are not conceptually similar. The word atheism describes not believing in the existence of gods but doesn't describe what the atheist does believe. It's analogous to saying this is a horse and that is not a horse. The only thing you know about the latter is that it's not a horse. Horse has a whole set of characteristics that are defined. You can't use those definitions to establish the characteristics of 'not a horse'. You can't ask 'horse' questions regarding 'not a horse' and expect coherent answers. For example, if you ask how many hooves 'not a horse' has, the response might be "none" or it has four "feet". So when you ask questions like how the atheist 'accounts' for the existence of evil (as in moral transgression), you are asking a 'horse' question because atheism doesn't doesn't ponder such questions nor does it account for the existence of such concepts. It has no tenets. It's 'not a horse'. All you can expect from that kind of question is either no answer or a pragmatic answer dealing with the possible causation of abnormal human behavior, which isn't what you were looking for. While some atheists adopt certain specific philosophies like humanism, existentialism or even nihilism, most atheists don't define their philosophical stance with that much specificity.