On Atheism and Brightness

I’m often told that atheists are really smart when it comes to religion. Then I read their replies to moral arguments for God’s existence and cry out, “WTF?”
Take this argument:

If no G, then no O.
But O.
Therefore, G.

Why the f&*^ would anyone think it’s even relevant to bring up X, Y, or Z?!?!?
Unlike some religious apologists, I don’t believe the explanation is either (1) atheists are willfully repressing the truth of God’s existence, or (2) atheists are stupid. Rather, my hypothesis is this: many atheists are so confident in their atheism that they have an extreme case of confirmation bias & don’t even take the argument seriously enough to use their brains and bother understanding it.
I could post numerous examples, but it’s really too depressing to go find them.