Of course, this situation is not unique to this country or to politics. People have to make choices every day, and they have to make them quick, but usually they do not have enough information on hand to weigh their options or even to comprehend what options they have. So they face another, much more fundamental choice - either do something based on the information they can obtain quickly or be paralyzed by inability to make any choice at all.
To overcome that dilemma, most people employ what some sociologists call "stock knowledge" or ready made beliefs, perceptions, prejudices, stereotypes, and rules of judgment that are taken for granted in a particular culture of community - without any questioning of their validity. Because using stock knowledge is an integral part of everyday life - people do it routinely and do not even try to use different modes of rationality, such as those used by scientists. The only thing that can change that is where "stock knowledge" does not work anymore and is producing results that are clearly and unambiguously false or against all expectations.
So the bottom line is that people will not make rational political decisions, not because they are incapable of making them, but because of the way human mind works to overcome the imperfect information problem. This is why democracy almost certainly degenerates into a mob rule unless some mechanisms are put in place that (i) limit the choices people can make based on the "stock knowledge" AND (ii) implement an effective alternative to "stock knowledge" to provide adequate information.
Wojtek
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It isn't just that people fall back on stock knowledge. They possess a stock worldview that is useful to them and has worked for them. They will ignore facts that contradict this worldview even if they aren't that difficult to come by. (Mark Danner in the "New York Review of Boooks" for January 19 points out that many Bush supporters weren't ignorant of claims that Iraq had no WMD, or that Osama had no connection to Saddam; they just chose not to give these claims any weight.) People aren't likely to abandon their long-cherished notions because of an untidy fact here and there; they must be jolted out of a stock worldview by a reality that overwhelmingly contradicts it. One reason that Americans have clung to archaic notions longer than Europeans, and seem so politically naive by comparison, is that history has thus far given them far fewer jolts. The biggest was the Great Depression, with the Vietnam War a close second. And, indeed, during those times, the Norman Rockwell Weltaunschung started to break down. But capitalism proved resilient enough to maintain and, it appears after this election, to strengthen it. Americans are made uneasy by the war and an uncertain economy, but not overcome by them. In these circumstances, it's hardly surprising that many of them will cling even more fiercely to comforting myths.