I read an interesting article recently about whether liberals are more intelligent that conservatives. The article was in The American, published by the libertarian American Enterprise Institute, so of course it's got a bit of an agenda. Still, it admits that many Republicans in the flyover states are probably not the sharpest knives in the drawer. (That's probably also true of a lot of Democrats across the country.)
Personally, I reject the contention that there is a correlation between intelligence and political beliefs. I do, however, thing that other attributes are generally more common in conservatives than liberals.
When I'm feeling bitter, I will say that conservatives are more selfish and evil than liberals. I'll say that conservatives don't care about anyone but themselves, and are too narrow-minded to understand the problems faced by people who are marginalized.
When I'm feeling a little more diplomatic, I'll say that conservatives are well-intentioned, but they don't look very far beyond the people they know and interact with on a regular basis. Conservatives worry primarily about their own families, friends, and neighborhoods. Liberals, on the other hand, tend to worry more about the environment, rights for the oppressed, and care for the poor. And of course, people who themselves are oppressed or poor tend to be liberals.
Still, intelligent people can and do have different perspectives on the world. And there are definitely conservatives who care about the world and want it to be as good as it can be. I personally just find it difficult to understand how social and fiscal conservatism is a path to a just and prosperous society. So maybe I'm the one who's stupid.