The theory of Rational Irrationality holds that it is often instrumentally rational to be epistemically irrational. In more colloquial (but less accurate) terms: people often think illogically because it is in their interests to do so.
An interesting implication emerges from the consideration of the mechanisms of belief fixation. Normally, intelligence and education are aides to acquiring true beliefs. But when an individual has non-epistemic belief preferences, this need not be the case; high intelligence and extensive knowledge of a subject may eve worsen an individual¿s prospects for obtaining a true belief (see chart below). The reason is that a biased person uses his intelligence and education as tools for rationalizing beliefs. Highly intelligent people can think of rationalizations for their beliefs in situations in which the less intelligent would be forced to give up and concede error, and highly educated people have larger stores of information from which to selectively search for information supporting a desired belief. Thus, it is nearly impossible to change an academic¿s mind about anything important, particularly in his own field of study. This is particularly true of philosophers (my own occupation), who are experts at argumentation.
The problem of political irrationality is the greatest social problem humanity faces. It is a greater problem than crime, drug addiction, or even world poverty, because it is a problem that prevents us from solving other problems.