As Eliezer has said, 9/11 is a "slam dunk", and I have no problem downvoting posts advocating ridiculous theories like creationism or conspiracy theories. Hopefully, this community agrees that 9/11 conspiracy theories are not worth considering.

I think that the question is still valid as a way to get clarification on what constitutes a "slam dunk". Eliezer seems to be using it in a way that doesn't exactly mean "not worth considering". He's also trying to delineate certain psychological types.