Atheists have been known to assert that most theists are "already an atheist as to all gods but your own" -- that is, that theists believe in one god while actively disbelieving in most of the thousands of gods which have ever been believed in by others. On this point, philosopher of atheism Sam Harris has often quoted the noted declaration of programmer Stephen F. Roberts, that:
I contend we are both atheists, I just believe in one less god than you do. When you understand why you dismiss all the other possible gods, you will understand why I dismiss yours.
And so the argument is that the very reasoning by which the atheist disbelieves in that one god which the theist happens to believe in, is the same reasoning as that theist applies towards gods other than their own. The fatal problem with this as an argument for atheism is that, for the theist -- and, indeed, for the deist, the pandeist, the polytheist, or the pantheist -- the essential matter is not really one of belief or disbelief in "gods" so much as it is about the characteristics of deity.

The paradigmatic example presented for a disbelieved god is usually one amongst the Greek or Norse polytheistic pantheons. But for the monotheist or the Pandeist to disbelieve in an asserted specific agency of Zeus or Thor is not to reject the notion of divinity, but to reject the inherent proposed characteristic of divinity being multiplied across multiple figures. Indeed, to the Hindu, an apparent multiplicity of Gods is totally reconcilable with there being one 'true' divine force, with all of the apparent ones simply being partial projections of the one underlying truth, or even egrigores created and empowered by the collective force of the minds of their human believers. With respect to more contemporary theologies, the atheist might counter acceptance of the JudeoChristian Bible with rejection of the Qur'an, or rejection of the Christian God with acceptance of a different exposition of the deity, be it Wiccan, Judaic, Bahai, Mormon, whatever. This even more acutely boils down to disputes over the characteristics of the deity, and not the fundamental existence of one.

The argument may be likened to the claim by the person who does not like any flavor of vegetable juice that a person who likes one kind but dislikes another ought, for the reason he dislikes the other, to dislike the first as well. Imaging the initial claim framed in those terms -- "when you understand why you dismiss other juices, you will understand why I dismiss yours." And, indeed, the atheistic formulation as applied to deities is even more arrogant than that, for unlike tastes in vegetable juices, which is at least understood to hinge upon subjective tastes, there is no objective certainty as to the existence or nature of deity. In that realm, there can only be speculation, and logical weighing and assigning of probabilities to various possibilities.

And so, the atheist who speaks of understanding one's own reasons for dismissing other theological formulations misses the point entirely, and fails to understand the distinction between examining different formulations, and rejecting the possibility of formulation itself altogether. Such a comparison, in the end, makes no more sense than claiming that understanding why one dismisses "2+2=5" and "2+2=3" ought to lead to an understanding of the dismissal of "2+2=4."