First and foremost, the dunce is incapable of valuing knowledge that they don't personally understand or agree with. If they don't know something, then that thing clearly isn't worth knowing.

There is a corollary to this that I've seen as well, and it dovetails with the way so many of these guys get obsessed with IQ. Anything they can't immediately understand must be nonsense not worth knowing. Anything they can understand (or think they understand) that you don't is clearly an arcane secret of the universe that they can only grasp because of their innate superiority. I think that this is the combination that explains how so many of these dunces believe themselves to be the ubermensch who must exercise authoritarian power over the rest of us for the good of everyone.

See also the commenter(s) on this thread who insist that their lack of reading comprehension is evidence that they're clearly correct and are in no way part of the problem.