Why do good people who join the Republicans turn bad?

Ezra Klein referred to an earlier publication of his that answers the question. A person who judges a government policy will tend to take the view that his political party takes, even if that is different from the judgement he or she would have made if the party took no position.

My favorite study (pdf) in this space was by Yale's Geoffrey Cohen. His experiment found the position of an individual's preferred political party overwhelmed both the objective policy content and the individual's preexisting beliefs. Cohen had a control group of liberals and conservatives look at a generous welfare reform proposal and a harsh welfare reform proposal. As expected, liberals preferred the generous plan and conservatives favored the more stringent option. Then he had another group of liberals and conservatives look at the same plans -- but this time, the plans were associated with parties.

Both liberals and conservatives followed their parties, even when their parties disagreed with them. So when Democrats were said to favor the stringent welfare reform, for example, liberals went right along. Three scary sentences from the piece: "when reference group information was available, participants gave no weight to objective policy content, and instead assumed the position of their group as their own. This effect was as strong among people who were knowledgeable about welfare as it was among people who were not. Finally, participants persisted in the belief that they had formed their attitude autonomously even in the two group information conditions where they had not."

As Ditto reminded me in an e-mail, sophisticated psychology isn't necessary for apprehending this tendency. Bertrand Russell had it long ago, when he said "If a man is offered a fact which goes against his instincts, he will scrutinize it closely, and unless the evidence is overwhelming, he will refuse to believe it. If, on the other hand, he is offered something which affords a reason for acting in accordance to his instincts, he will accept it even on the slightest evidence."

In other words the political party's judgement on an issue will dominate no matter what the individual would have concluded on their own. But going along with that the individual will believe that they came to that conclusion independently and will probably react negatively if someone else suggests they are not thinking for themselves.