I think they’re just determined to cringe at literally anything they ever see. The “edge” here is just a choice of humor style.

And calling theists morons is pretty easy seeing that they can obviously easily fall for anything. Believing in God in and of itself is just a blip of ignorance, and we all have a million of those. But the fact it leads to so many other wrong beliefs makes it correct.

In other words, they’re not a moron for being a theist, but being one will make them a moron.