The problem with democrats is similar to the problem with islam... there is a vast shortage of those willing to eschew the radicals of their group.
I am a registered democrat and I think Joe is a hateful piece of human excrement. I hope I eschewed that one hard enough.
I do agree that here is often a shortage of those willing to criticize the radicals, though, and I would even go so far as to state that opinions presented on messageboards can give the impression that "liberals" are just a bunch of anti-American leftists like we too often see here, but that is just because the internet tends to bring out the extreme instead of the more intelligent and moderate.
Since you brought up Islam, though, I tend to use the reaction to it as the barometer for establishing who is and who isn't applying liberal political principles to their world view. True liberals see Islam for what it is -- a profoundly conservative ideology that stands in diametrical opposition to just about every liberal principle imaginable. A leftist, on the other hand, sees it as their prime directive to defend Islam because they see all their little mates doing so and because the enemy of their enemy is their friend -- their enemy in this case being Western civilization.