Dave nails another one.
Unfortunately this research shows the reasons why living in Seattle will make you liberal, and living in Colorado Springs will make you conservative. Extremism and the resulting biases are environmental.
I was thinking about this in the context of the hullabaloo (is that a word?) over intelligent design and evolution. By going to court to effectively silence the ID crowds, the evolution theorists are creating their own legally enforced "deliberation with like-minded peers." It occurred to me earlier that the way to silence or to counter a false science is not to censor one side, but rather exposure of both sides to what can be known. We didn't get past "the earth is flat," "tomatoes are poison," and "waltzing causes plague" by censoring people and calling them names, but rather by opening up society to more information.
But having the information available is not all it takes. Much like the book buying illustration shows, there is also research to show that the explosion of information sources deepens the divide as well. People who are leaning in one direction or the other gravitate toward information sources that reinforce their views, and shun those that counter their view.
I second Dave's conclusion. Find idiots, and talk to them! You will make the world a better place.