why politics make people stupid

[watertank]

...citizens' interpretations of events are slanted toward their previously held convictions. Evidence for this phenomenon is drawn from a variety of sources. In Lord et al's classic experiment (1979), opponents of the death penalty were more likely to find fault with a study suggesting that it deters serious crime; death penalty supporters were similarly resistant to a study that drew the opposite conclusion. In fact, exposure to discordant evidence only made people more set in their ways.
Alan Gerber and Donald Green. MISPERCEPTIONS ABOUT PERCEPTUAL BIAS. Annual Review of Political Science, Vol. 2: 189-210 (Volume publication date June 1999) (doi:10.1146/annurev.polisci.2.1.189)

facts that do not conform to one's views make her more certain in her beliefs. extremely strong evidence or external influence is required to overcome a perceptual bias.

http://rioken.livejournal.com/54668.html