Mark Twain once said something to the effect that it's not what you don't know that gets you into trouble; it's what you know for sure that just ain't so. This is what I'd like to add to the discussion going on among Jon Chait, Julian Sanchez, and Matt Yglesias on the right's "epistemic closure," the belief that the only sources of information that can be trusted are those that exist within your movement.
As someone commented somewhere along the way, the difference between the left and the right isn't that the left doesn't have its own ideological information sources but that they see these as an addition to those sources that do actual news-gathering, not a substitute for them. Progressives like Rachel Maddow, but nobody thinks that if you watch her show, you now no longer need to read the newspaper or listen to NPR to understand what's going on in the world. Quite a few conservatives, on the other hand, believe that if you're listening to Rush Limbaugh or watching Glenn Beck, then they'll tell you everything you need to know. And of course, one of the things people like Limbaugh and Beck are constantly telling their audience is don't pay attention to the mainstream media, because they're filling you with liberal lies.
The result of this difference is where the Twain quote comes in. While there may be "groupthink" that happens on the left, what you don't generally get is huge numbers of progressives gripped by beliefs that are simply factually untrue. This happens all the time on the right. We found weapons of mass destruction in Iraq. Barack Obama isn't a U.S. citizen. The health-care reform bill contains a provision for death panels. The reform mandates the hiring of 16,000 IRS agents who will be coming to arrest you if you don't get health insurance.
There are a number of important things to understand about the discourse in places like Fox News and the conservative talk-radio universe, but one of the most crucial is that misinformation circulates through them and gets validated by not only the hosts but by cynical figures like Newt Gingrich who are willing to lie to people if they think it will benefit their side politically. And since so many of their supporters get information only from within that closed system (or willfully discount any information they get from without it), it doesn't matter if sources like Politifact eventually point out the falsehood.
It's hard to have a rational debate if the two sides have different values and priorities. But if they can't agree on what the facts are, it becomes virtually impossible.
-- Paul Waldman