And there is nothing illogical about that for a monotheistic believer. If Allah exists, then Zeus, Thor, and the Great Spirit do not.

The strange thing is how many of us atheists think that this should be convincing to a theist. This quote should be just as convincing to a christian as bible passages are to an atheist. We don't approach the question of the existence of a deity in the same way.

The reason they dismiss all other possible gods is because they believe in a monotheistic god. They understand that perfectly well, and the answer you hear, "Mine is the real one", is exactly what they should say to refute your point.

They understand why they don't believe in Zeus. You can ask them: "Why don't you believe in Zeus?" "Because I believe in Yahweh." Perfectly logical answer.

That's why I loathe this quote. It assumes that if a theist stopped believing in Yahweh, then he'd be an atheist. That would mean that you'd never see a christian convert to a muslim, or whatever. Interestingly, with just a slight modification, you can make the quote reasonable again.

When you understand why I dismiss all the other possible gods, you will understand why I dismiss yours.

Of course, then the quote loses much of its apparent convincing argument.