Human Factors and political partisanship.
The NYT has a great article today (www.nytimes.com/2006/01/24/science/24find.html?_r=2&pagewanted=print) that tells us something about confirmation bias. When people listened to political speech that they disagreed with, they rejected it. But this rejection was not based on logic, it came from the emotional center of their brain and excited their pleasure area. In other words, when we hear something that we disagree with, we don't even give it a chance. We just reject it outright. And even worse, we get pleasure out of rejecting it, so we are more likely to reject similar situations in the future.
This explains a lot to me about the popularity of reality TV, talk radio, and lots of other media that I always find ridiculously asinine. Even people who hate it, watch it so that they can reject it. So the ratings are high and it stays on.