But I could just as well be any religion that predates Christianity if the "boob rule" were my only method for choosing a faith. I'm athiest because I'm way too into science. Once you start to learn a lot about biology and/or organic chemistry, and look at some of the synthesis experiments, it's impossible to believe the fairy tale of any god.
Even in a historical sense, no one is Odinist anymore, no one still thinks the sun god pulls up the sun with his chariot, no one still believes in Zeus or Thor or Ra. Its a fate that will befall Christianity/Islam/Judaism as well. Just because they are the three dominant religions now does not mean anything for the future. There were many a dominant religion in the history of man....but the "newest" mainstream three are believed to be the "eternal truth" now, just like so many others were in the past.