I do not think Dawkin's ever makes a claim about the superiority of atheism, in terms of being a 'better person'. He only claims organised religions can be detrimental to society but also freely admits people like Stalin\Hitler, alleged Atheists (debatable), didn't necessarily have religious incentives for their attrocities. I believe he actually steers away from 'betterness.' His stance, I believe, is along the lines that organised theism is perhaps more detrimental than human propensity.