Neither I nor any other atheist needs to have been a theist beforehand in order to have reached our present position, if that's what you're trying to argue. All that is required to adopt the stance of identifying as atheist is the existence of theists. You hold a set of beliefs; I happen not to share them. It really doesn't get more complicated than that.
At the age of five, Skagra decided emphatically that God did not exist. This revelation tends to make most people in the universe who have it react in one of two ways - with relief or with despair. Only Skagra responded to it by thinking, 'Wait a second. That means there's a situation vacant.'
