We doctors like people to think we know what we're talking about, and may be so convincing that we convince ourselves too. Because other people's lives depend on it, we have a big emotional need to be right and are uncomfortable with the thought that none of us really knows enough to be a good doctor….
Scientists, on the other hand, are very comfortable with the unknown; it is their bread and butter. When scientists disagree there is no more at stake than the scientists' amour propre, whereas medical disputes get rancorous because forever in the background is the thought that the other chap is damaging patients.
Science does not in itself make its practitioners haughty (the contrary, if done honestly), whereas medicine does. The main reason for that, I think, is because doctors get used to seeing other people undressed while they themselves are clothed. Once you have seen dukes and archbishops in their underpants they're never quite the same again.
[Thanks to Jeff Schaler for the links.]