Matthew Yglesias makes an excellent point about the way in which people confuse vulgar or strident rhetoric with extreme ideology:

Joe Klein’s “you might be a left-wing extremist if…” list is quite revealing. A number of his items are somewhat strawmannish substantive positions. Many of them, however, rather plainly have nothing whatsoever to do with extremism of any sort. To wit:

1. Dismissively mocks people of faith, especially those who are opposed to abortion and gay marriage.
2. Regularly uses harsh, vulgar, intolerant language to attack moderates or conservatives.

I mean, there’s a term for people who express left-of-center views in a vulgar manner and it isn’t “extremist” — it’s vulgar. The sentiment “that asshole Bush ruined the balanced budgets of the 1990s all for the sake of his fucking tax cuts” is perfectly centrist. Similarly, whether or not you tend to mock people you disagree with about matters of religion is just a matter of politeness. But rudeness has no ideology. Under certain circumstances, of course, it’s important to maintain a certain standard of politeness, but there’s no reason to elevate this to a core ideological point.

This is the same mistake that many people make in analyzing Paul Krugman, for instance, who was portrayed as some sort of crazed leftist for his strident opposition to the Bush administration. But Krugman is a trained economist who won the prestigious John Bates Clark medal and was, until recently, known as a moderate Democrat. Similarly, Atrios (aka Duncan Black) is an economist with (basically) center-left policy views. Rhetorical and ideological extremism may tend be correlated, but extreme rhetoric doesn’t make one an ideological extremist.