Watching Jonathan Alter on with Maddow I'm reminded of an additional importance of having liberal hosts (radio and tv), aside from the fact that maybe they'll actually reach some viewers at home. I think that unless you really steel yourself for combat mode, it's generally human nature to try to find common ground with people you're talking to. So when people go chat with O'Reilly or Hugh Hewitt they're, to some degree, trying to find those areas of agreement. When mainstream center lefties like Alter go on Maddow's show, they're much more likely to be aggressive advocates of a more liberal position than they would otherwise. Host approval helps reinforce the view.
Franken used to do this on his radio show, though I think his sensibilities were always just a little bit too in line with such people for it to be as effective.
