Well if I understand your question correctly your asking me how people become atheist, and for me: I'm nihilist (Hardcore atheist). I just started seeing how if there was a god .. he is hateful. Look at this world: its full of death, violence.. its endless. So much for an "all loving god" eh? But really it's just seeing how people are scared of hell and getting out of that trend of being scared of it. If that doesnt your question, sorry. The ancient Greeks began to consider that maybe the gods were just human inventions. Protagoras (490- 420 BC) said: "As to the gods, I have no means of knowing either that they exist or do not exist" which we would today consider to be atheist. He was followed by Aristotle, Epicurus, and many others. There may have been atheists before that, but their names have not come down to us.