I would venture a guess that atheists who haven't put thought into the possibility of there being a god are significantly in the minority. Although there are some who dismiss the notion as an impossibility, or such a severe improbability as to be functionally the same thing, in my experience this is usually a conclusion rather than a premise, and it's not necessarily an indictment of a belief system that a conclusion be strongly held. Some Christians say that "all things testify of Christ." Similarly, Avicenna was charged with heresy for espousing a philosophy which failed to affirm the self-evidence of Muslim doctrine. But cultures have not been known to adopt Christianity, Islam, or any other particular religion which has been developed elsewhere, independent of contact with carriers of that religion. If cultures around the world adopted the same religion, independently of each other, that would be a very strong argument in favor of that religion, but this does not appear to occur.

Many people here are grew up in religious settings. Eliezer for example comes from an Orthodox Jewish family. So yes, a fair number have given thought to this. [...] Curiously many different people believe that they've been contacted by God, but they disagree radically on what this contact means. Moreover, when they claim to have been contacted by God but have something that doesn't fit a standard paradigm, or when they claim to have been contacted by something other than God, we frequently diagnose them as schizophrenic. What's the simplest explanation for what is going on here?