A couple of years ago my Adult Bible Fellowship teacher (Ken Best) mentioned that people are wired such that the feedback they get from life tends to reinforce (or confirm) their prior opinions, and that's because how we process information depends on what we think it will tell us. I have to say I agree with this observation. Generally, it takes something big (e.g. 9/11) to cause such a disconnect that we actually reexamine our prior opinion, but normally we see what we expect to see and disregard the rest.
Mickey Kaus has championed the Faster Feiler Thesis, which essentially is that we have speeded up both the information flow and its processing for people. And I have to say I also agree with this.
Put the two together, and what do you get - increased polarization. Our opinion is converted from jello to cement in ever faster times. And if there are two sides to every argument, then we have two sides set like epoxy around every policy, every politician, around pretty much everything (those Taste Great/Less Filling ads aren't so funny now). Not only do we process the increased information flow faster, the increased flow drives us to become set in our positions ever faster.
Sound like real life? Perhaps how Bush Derangement Syndrome can become both widespread and hard to cure so quickly? Perhaps why so many people seem to be so completely convinced that they are not just right, but so right that any disagreement can only spring from impure motives -- or you're not just wrong, you're evil.
Even 9/11 only reset folks for perhaps 24 hours. I can recall on 9/12 that a many people (at least many people on TV) had started to use it to support whatever they had been in favor of prior: ballistic missile defense, global warming regulation, supporting Israel, abandoning Israel, ...
9/11 had become another proof point for their existing biases.