Now, that's stupid.
They come to different conclusions about the dangers of Islam because they start with different premises. That's not to say they are stupid. That is to say they are wrong, though.
Some people, like the 'president lied' crew, do have a pathological affliction. It's not stupidity, exactly. They just start with their conclusion and work backwards, rather than start with the evidence and come to conclusions. That's certainly not smart, and it does seem stupid, but I think it's more a mental affliction than anything else.