A person is said to exhibit rational irrationality when it is instrumentally rational for him to be epistemically irrational. An instrumentally rational person chooses the best strategies to achieve his goals. An epistemically irrational person ignores and evades evidence against his beliefs, holds his beliefs without evidence or with only weak evidence, has contradictions in his thinking, employs logical fallacies in belief formation, and exhibits characteristic epistemic vices such as closed-mindedness. Epistemically irrational political beliefs can reinforce one’s self-image; boost one’s self-esteem; make one feel noble, smart, superior, safe, or comfortable; and can help achieve conformity with the group and thus facilitate social acceptance. Thus, epistemic irrationality can be instrumentally rational.

If I falsely believe the road I am crossing is free of cars, I might die. So I have a strong incentive to form beliefs about the road in a rational way. However, if I falsely believe that import quotas are good for the economy, this has no directly harmful effects. (On the contrary, the belief can have significant instrumental value. It might make me feel patriotic; serve my xenophobia; serve as an outlet to rationalize, sublimate, or redirect racist attitudes; or help me pretend to have solidarity with union workers.) … Epistemic rationality is hard and takes self-discipline.

When it comes to politics, individuals have every incentive to indulge their irrational impulses. Demand for irrational beliefs is like demand for most other goods. The lower the cost, the more will be demanded. The cost to the typical voter of voting in epistemically irrational ways is nearly zero. The cost of overcoming bias and epistemic irrationality is high. The psychological benefit of this irrationality is significant. Thus, voters demand a high amount of epistemic irrationality.

Jason Brennan, The Ethics of Voting, p.173-74