Polarization and Confirmation Bias
"The facts are being fixed around the policy." So observed British Foreign Secretary Jack Straw (in the infamous "Downing Street Memo") about his conclusion that Bush and Cheney had long ago decided to invade Iraq but were now, after the fact, manufacturing justifications to support that policy. This was a major act of deception, to be sure, but I think that when it comes to politics we all do something like this on a small scale. Once we make our decision why we reject one candidate but support the other, or make the decision to be a Democrat as opposed to a Republican, we set about, or continue, looking for the facts that confirm our decision as to why X is good and Y is bad. Polarization then occurs when we think we have reached our conclusions in good faith but the others have not, for if they were acting in good faith how could they not agree with us?