Libertarians tend to think conservatives are idiots. Sort of the way many athiests feel about deists. Same dynamic. Probably stems from the size of the differing demographics.

One side is a small minority, consisting disproportionately of unusually intelligent people, the other is the majority of the population. There are many more highly-intelligent people in the majority, but you are less likely to encounter them because they are in a more heterogenous group.

Highly-intelligent conservatives don't suffer from this "random-sampling" bias because they tend to know each other, so they're surprised when people are astonished at how intelligent they, personally, are.