I've often read this quote from John Stuart Mill without really thinking much about it, other than that it seemed so obviously true.
I never meant to say that the Conservatives are generally stupid. I meant to say that stupid people are generally Conservative. I believe that is so obviously and universally admitted a principle that I hardly think any gentleman will deny it. -- John Stuart Mill
Now we have empirical proof that this is true: a study published by Psychological Science.
Despite their important implications for interpersonal behaviors and relations, cognitive abilities have been largely ignored as explanations of prejudice. We proposed and tested mediation models in which lower cognitive ability predicts greater prejudice, an effect mediated through the endorsement of right-wing ideologies (social conservatism, right-wing authoritarianism) and low levels of contact with out-groups. In an analysis of two large-scale, nationally representative United Kingdom data sets ( = 15,874), we found that lower general intelligence ( ) in childhood predicts greater racism in adulthood, and this effect was largely mediated via conservative ideology. A secondary analysis of a U.S. data set confirmed a predictive effect of poor abstract-reasoning skills on antihomosexual prejudice, a relation partially mediated by both authoritarianism and low levels of intergroup contact. All analyses controlled for education and socioeconomic status. Our results suggest that cognitive abilities play a critical, albeit underappreciated, role in prejudice. Consequently, we recommend a heightened focus on cognitive ability in research on prejudice and a better integration of cognitive ability into prejudice models.
The full study can be found here. This is rather scary stuff, I think; it means that no matter how you try to educate conservatives, there's not much chance they'll change their minds, because they prefer feeling safe, and sticking to the status quo, over actually thinking.
John Dean's book Conservatives Without Conscience also has an excellent take on this whole phenomenon. I highly recommend it to anyone who wants to learn more about the conservative mindset.