I find atheism to be a device for regaining one's personal power after a debilitating encounter with religious authority.
What about people that don't beleive in God ever? Or are you specifically referring to once religious people that become atheist? If so, my question is moot.
As for me....I don't even see why someone needs an argument for atheism or to believe in god. I say "who cares what you believe as long as you aren't trying to effect my life with it?" Of course, that last bit, about trying to impose standards on others when they don't have the same belief, that's wrong whether one is an atheist, christian, muslim, taoist, or just cranky old neighbor.