quote: To me, the extreme conservatives and the extreme liberals are the ones who don't think. An extreme conservative will agree with the Swift Boat veterans' accusations against Kerry because they're conservative and Kerry's liberal, not because of any evidence.
I'm afraid that a useless criterion. While the pack-mentality you describe is a real phenomenon (Michael Goldfarb recently described US politics as being like that of a middle eastern bazaar - you believe your friends and disbelieve your enemies) it makes a mockery of the word "extreme". None of these are extreme positions - they are merely PARTISAN positions.
Extreme is a qualitative statement comparing two referents. It would be valid to say that in a given political climate, the right wing supports, say, privatisation, and the left wing supports nationalisation. The extreme positions here would be "... of everything"; the moderate positions here would be "... of certain things".
It is invalid to attribute extremism to someone just because they hold a partisan position you do not share - that in fact is an ad hominem slander. And it arises only because of the modern doctrine that ineffective "moderates" are some sort of pinnacle of uselessness to aspire to.
"Extremist" has become a political insult rather than a description of a position precisely in order to dismiss certain positions without analysis.