Preposterous Sagan Quote
According to Carl Sagan (mentioned in a comment on Respectful Insolence):
In science it often happens that scientists say, “You know that's a really good argument; my position is mistaken,” and then they would actually change their minds and you never hear that old view from them again. They really do it. It doesn't happen as often as it should, because scientists are human and change is sometimes painful. But it happens every day. I cannot recall the last time someting like that happened in politics or religion.
It isn't unheard of for people to change their political or religious opinions. In the case of religion, that's known as conversion. In the case of politics, there's the common phenomenon of former liberals who became conservatives on September 11, 2001