[Bork]

Supposed evidence for Y: The smarter you are the more likely you are to believe Y.

I don't think that alone is enough to justify belief that Y IS true. However, at least in general it does make it more likely that Y is true, so assuming we have no other evidence then we are justified in believing Y is probably true. We started with 50% confidence Y was true, now we have some evidence that Y is true so our confidence should increase.

One potential problem would be certain beliefs which say 3% of brilliant physicists believe to be true and the rest believe to be false. For such a belief the smarter you are the more likely you are to believe it's true, and the more likely to believe it's false. This is because the only people that believe either way are brilliant physicists.