John Holbo in Crooked Timber:
One place to start is to ask why it is that people, as individuals, gravitate to certain moral and political viewpoints. Jonathan Haidt’s “moral foundations” theory—which shows that conservatives and liberals have different moral sensibilities, sensitive to different moral considerations—is perhaps the best-known account. But there are others.
In a 2012 piece for the Economist, I surveyed some of the research in personality psychology that indicates a correlation between political ideology and a couple of the “Big Five” dimensions of personality—conscientiousness and openness to experience, in particular—and then connected that to evidence that people have self-segregated geographically by personality and ideology. It’s an interesting post and you should read it.
The upshot is that liberals (low conscientiousness, high openness to experience) and conservatives (high conscientiousness, low openness) have distinctive personalities, and that there’s reason to believe we’ve been sorting ourselves into communities of psychologically/ideologically similar people.
Wilkinson goes on to talk about other, non-Haidt stuff that contributes to polarization. I like that better. (I think Wilkinson does, too.) But I want to grouse about Haidt, who I think has done interesting empirical work but who commits what I regard as terrible howlers when it comes to moral theory, and when it comes to reasoning about practical, normative implications of his work.
More here.