Matt Taibbi has been focused on this lately. His theory is that polarization and writing for one side makes more money. He's done a few scathing articles about the mainstream media's abandonment of traditional media values of impartiality (as much as they can be) and not publishing innuendo and rumor.

Some of his work is pretty insightful, especially the time when the gov't leaked to a reporter, who wrote a story, and then the gov't got a search warrant by pointing to the article and saying "see, there is something here!".