Why does theism can lead a few theists to be less intelligent than they could be if they opened their mind and understood unbelief in gods?

Ignorance isn't hard to understand, but obviously it will never be accepted by people of knowledge.

I don't know if you're a poe

or just the most ironic atheist in the history of atheism.

You mean like you?

Not knowing something has never been considered MORE intelligent.

You still need to provide a citation!  Otherwise, all you are doing is proving that the questioner is less intelligent!  

FYI:  If you know how to phrase your question there are peer-reviewed studies on such things, but it's useful if you do your own homework!

Go back to school. That is, assuming you have ever been to one.