Stop Me Before I Vote Again

I posted a comment on the Guardian's site about Gary Younge's Jesse Jackson article, in which I pointed out the disconnect between the politics of the rank-and-file and those of the office holders. Here was one of the responses to that comment:

I'll avoid the political science jargon, but look up the median voter theorem -- it explains why, in a first-past-the-post system, two-party politics is most likely and the two parties are likely to adopt effectively similar platforms. It has nothing to do with corruption, just with the need to get 50% +1 of the total number of votes cast. It doesn't matter *how much* your supporters actually like your position, just that more of them like your position than that of your opponent. Representatives are often "unrepresentative" of their constitutents; American blacks tend to be social conservatives, uncomfortable with homosexuality and abortion, yet black Congressmen are overwhelmingly in favour of gay and reproductive rights.