Simple. Right-wingers tend to occupy the middle of the intelligence spectrum while left-wingers occupy the lowest and the highest (at least Democratic voters as a whole; many of the less intelligent Democrats don't understand liberal vs. conservative). However, the lower-middle end, in which many of these comments are from, is generally more conservative (note that Atlas, both left and right, is at the upper end of intelligence).
There's a spectrum Atlas Forum is at the upper end of, but I don't think it's intelligence.
