This thinking is a memetic poison created by the exact people that need to be shamed out of the public discourse. I used to agree with it, but seeing how it's been coopted by the bigots, I reject the premise entirely.
No one is calling Christians stupid. The nutjobs that want to tear down our secular society and replace it with a white Evangelical ethnostate are telling Christians that their political rivals are calling them stupid. They're the suckers for the conmen, and at this point, it's not worth attempting to rationalize debate.