Has anyone been mocked out of faith who wasn't already on the precipice of doubt?
As stated, Zach's supposed zinger isn't an atheist/agnostic argument per se. It could be merely an argument for religious tolerance ... except that it's from a Facebook page titled DoubtGod. So is he a skeptic only where Yahweh is concerned? Oops — send it back to the script department for a rewrite.
The skeptic's argument, as I've seen it, is, "The world's religions can't all be right, but they can all be wrong." That doesn't exhaust the possibilities, though. One can be the closest to the truth of the Way Things Really Are, and others can be further away to varying degrees. One of the gods can be real, and the rest shadows and reflections of him (or Him). This is what a better-educated believer will say in response; the simpler believer will merely assert that all the others are false. Either way, the skeptic's argument is a kind of cross of St. Anselm's ontological argument turned upside-down and Murphy's Law: "If all religions can be wrong, they are all wrong." The consequent doesn't necessarily follow from the antecedent.
If a person has what he believes are good and sufficient reasons to believe that a particular god — or pantheon of gods — is the only one that's real and true, then pointing out that there are 4,999 other gods he could worship is useless; it's like pointing out that there are over 200 other countries in which he could live, or 500 other microbrews he could prefer, or 60 million other women he could love. So what? What compelling reasons can you offer that will cause him to move, or switch brands, or get a divorce? Even better, what compelling reasons can you offer that will get him to stop drinking, or stop loving women, or commit suicide?
In any event, Zach, this isn't a one-line wrecking ball; it isn't even the beginning of an argument. It's a rather pitiful and immature sneer.