"You're right when you say a correlation of intelligence with liberalism is evidence for liberalism, but that's not because the stupid people are conservative, it's because the smart people are liberal."

That seems to me exactly wrong. A proposition's truth or falseness is not entangled in the intelligence of the people who profess the proposition. Alien cultists do not change the probability of poorly hidden aliens. Dumb people who argue for evolution over creationism do not raise the probability that Genesis is natural history, no matter how dumb they are. Conservative Proposition X will be true or not true regardless of whether it is supported by a very intelligent conservative or by a very dumb conservative.