I think you have a good point. How often do we complain about liberals tossing around adjectives like racist, homophobic, bigoted, class-biased, moron while at the same time cheering when people like Coulter go and do the same with words like treason, liar, moron.
Sullivan goes too far (and he really isn't one to complain when it comes to his rhetoric against people who refuse to say that unnatural behavior is OK) in denouncing Coulter.
There is definitely a place for Coulter in the right's public face but to say that she convinces people is just not true. I have given her book Slander to relatively nonpolitical conservatives who didn't like it because of all the invective she's always using.
Sometimes, I get the impression that she writes as hyperbolically as she does as part of an act. That said, she is a great TV presense because she usually tones down her words and is a quick wit. Ann Coulter is a good defender of conservative causes but she's never said anything original that I've seen. There's a lot better analysts on this forum, IMHO.
One big difference is in accuracy of the charges. If a person is known to deliberately make untrue statements he is a liar. If one takes a stand that aids the enemies of this country, he is by definition, treasonous. These are not slanderous terms or terms tossed about for the purpose of being inflammatory. They are accurate depictions of those who promote the liberal/socialist agenda. The term moron, might be a little over the top, but only for the simple reason that the technical definition of moron doesn't apply, but to say that many are ignorant is absolutely truthful.