Why is politics a subject matter about which there is widespread, strong, and persistent disagreement? In this paper, the philosopher Michael Huemer (following Bryan Caplan) argues that the phenomenon of rational irrationality is (a large part of) the answer to this question. In short, the idea behind rational irrationality is that people can rationally adopt irrational beliefs because acquiring rational beliefs involves a "cost" that exceeds its benefit. There are certain things that people want to believe "for reasons independent of the truth of those propositions or of how well-supported they are by the evidence". Given this there is a cost to thinking rationally, "namely, that one may not get to believe the things one wants to believe". The idea is that "most people will accept this cost only if they receive greater benefits from thinking rationally". And since there are almost no benefits to be received from thinking rationally about political issues, we can predict that many people will often be irrational about politics (and it is easy to find examples where this prediction holds true).
Elaborating on the theory of rational irrationality, Huemer appeals to the distinction between instrumental rationality and epistemic rationality. Roughly, while instrumental rationality consists in choosing the best available means to the ends one has, epistemic rationality consists in forming beliefs in a truth-conducive manner (accepting only things that are well-supported by evidence, revising beliefs in the light of new evidence, avoiding contradictions and logical fallacies, etc.). With this helpful distinction at hand, Huemer says that the theory of rational irrationality holds that it can be instrumentally rational to be epistemically irrational.
In order to explain why some people adopt irrational beliefs, we need only assume that these people prefer to believe certain things to a higher degree than they prefer to be epistemically rational. Huemer points out that for some people, being epistemically rational may itself be preferred with sufficient strength to outweigh whatever preferences they might have with respect to their beliefs, but for many people this will not be the case. Huemer argues that the phenomenon of rational irrationality is particularly common when it comes to political beliefs.
As argued by Caplan, voters have systematically biased beliefs about economics. The policies that voters choose are, for example, systematically less free market and more anti-immigrant than what would serve the those voters own ends. But because of the miniscule chance that a single vote makes any difference to the outcome, it can be rational for the individual to indulge in irrationality in the political domain. Like Caplan, Huemer considers the competing explanations for political disagreement and concludes that neither of them (separately or jointly) can fully explain the salient features of political disagreement (without appealing to the phenomenon of rational irrationality). The commonly given explanations include that political issues are unusually difficult, that people are ignorant, and that people have different fundamental value systems. No doubt, these things are true as well (at least the second two), but they are not sufficient to explain disagreement. Commenting on the view that disagreement might be due to there not being any objectively true answers to value questions, Huemer boldly states that "value questions are objective, and moral anti-realism is entirely unjustified". I strongly disagree with him on that point (I think it is realism that is unjustified), but I agree that many political disagreements cannot be fully explained that way.
The irrationality hypothesis is superior to alternative explanations of political disagreement in its ability to account for several features of political beliefs and arguments: the fact that people hold their political beliefs with a high degree of confidence; the fact that discussion rarely changes political beliefs; the fact that political beliefs are correlated with race, sex, occupation, and other cognitively irrelevant traits; and the fact that numerous logically unrelated political beliefs—and even, in some cases, beliefs that rationally undermine each other—tend to go together. These features of political beliefs are not explained by the hypotheses that political issues are merely very difficult, that we just haven’t yet collected enough information regarding them, or that political disputes are primarily caused by people’s differing fundamental value systems.
Why do people have preferences over beliefs? Huemer's answer is that
The beliefs that people want to hold are often determined by their self-interest, the social group they want to fit into, the self-image they want to maintain, and the desire to remain coherent with their past beliefs. People can deploy various mechanisms to enable them to adopt and maintain their preferred beliefs, including giving a biased weighting of evidence; focusing their attention and energy on the arguments supporting their favored beliefs; collecting evidence only from sources they already agree with; and relying on subjective, speculative, and anecdotal claims as evidence for political theories.
Here I feel that this otherwise excellent paper tells only half the story. It is reasonable to ask why people are self-interested (and besides, it is in general not true that they are, especially not in the voting booth); why people want to fit into social groups; why we are more prone to be biased in certain directions (and not in others), etc. Our cognitive biases and preferences are not random and there is an evolutionary story to be told about how and why they came about (as Caplan noted). As Steven Pinker said in The Blank Slate,
Our minds keep us in touch with aspects of reality – such as objects, animals, and people – that our ancestors dealt with for millions of years. But as science and technology open up new and hidden worlds, our untutored intuitions may find themselves at sea.
For many domains of knowledge, the mind could not have developed dedicated machinery, the brain and genome show no hints of specialization, and people show no spontaneous intuitive understanding either in the crib or afterward. They include modern physics, cosmology, genetics, evolution, neuroscience, embryology, economics, and mathematics. It’s not just that we have to go to school or read books to learn these subjects. It’s that we have no mental tools to grasp them intuitively.
Understanding in these domains is likely to be uneven, shallow, and contaminated by primitive intuitions. And that can shape debates in the border disputes in which science and technology make contact with everyday life. […] with all the moral, empirical, and political factors that go into these debates, we should add the cognitive factors: the way our minds naturally frame issues. Our own cognitive makeup is a missing piece of many puzzles, including education, bioethics, food safety, economics, and human understanding itself.
Huemer does provide a nice list of things we can do to try to overcome our biases, but learning about the evolutionary origins of our cognitive biases should be added to his list as it may well be essential to overcoming bias. Still, Huemer's paper is very well worth reading in addition to Caplan's excellent book The Myth of the Rational Voter.
Here is a short clip where Huemer talks about why people are irrational about politics: