Christians and atheists: who's more threatened by whom?

In his column for Newsweek, Rabbi Marc Gellman advances the thesis that atheists are "threatened" by the idea of God:

I don't know many religious folk who wake up thinking of new ways to aggravate atheists, but many people who do not believe in God seem to find the religion of their neighbors terribly offensive or oppressive, particularly if the folks next door are evangelical Christians. I just don't get it.

You know, I have precisely the opposite impression regarding theists. I have the impression that theists would find my atheism more affronting than they would find the beliefs of theists who happen to observe other faiths. Though it may surprise you to hear it, given the content of my blog, I tend not to be as "open" about my atheism in public (I also don't want to harm my employment prospects)--not knowing who I might offend inadvertently by discussing it.

But I cannot conceive how an atheist would find the idea of God more "threatening" than he or she would the idea of Santa Claus, the Tooth Fairy or the Celestial Teapot. Can anyone help me out, here?

Gellman continues:

This must sound condescending and a large generalization, and I don't mean it that way, but I am tempted to believe that behind atheist anger there are oftentimes uncomfortable personal histories. Perhaps their atheism was the result of the tragic death of a loved one, or an angry degrading sermon, or an insensitive eulogy, or an unfeeling castigation of lifestyle choices or perhaps something even worse.

Or maybe, just maybe, it has something to do with the lack of evidence for God's existence? Whaddya think?

UPDATE: See also this post on Philaletheia.

UPDATE II: Please spare a few moments to complete this Post-Purchase Deity Evaluation Form. (Via Pharyngula)