I just watched Letterman do an excellent interview with Rachel Maddow. One of Letterman's questions got to the core issue about the false equivalencies being made between Fox and MSNBC. It's not about having a viewpoint. It's about one network having some standards of accuracy and the other being a routinely deceptive propaganda machine.
Letterman and Maddow both make excellent points about the media. The whole interview is worth watching if it's posted. Here's a big chunk of it.
Why is it that all the best critiques of the news industry are happening on comedy programs?