Political extremism is supported by an illusion of understanding.

Fernback et. al. start their interesting article with some nice quotes:

Bertrand Russell “The opinions that are held with passion are always those for which no good ground exists.”

Clint Eastwood “Extremism is so easy. You’ve got your position and that’s it. It doesn’t take much thought.”

Here is their abstract, followed by a bit on the experimental details:

People often hold extreme political attitudes about complex policies. We hypothesized that people typically know less about such policies than they think they do (the illusion of explanatory depth) and that polarized attitudes are enabled by simplistic causal models. Asking people to explain policies in detail both undermined the illusion of explanatory depth and led to attitudes that were more moderate (Experiments 1 and 2). Although these effects occurred when people were asked to generate a mechanistic explanation, they did not occur when people were instead asked to enumerate reasons for their policy preferences (Experiment 2). Finally, generating mechanistic explanations reduced donations to relevant political advocacy groups (Experiment 3). The evidence suggests that people’s mistaken sense that they understand the causal processes underlying policies contributes to political polarization.

Each of the experiments recruited 100-200 U.S. residents. In the first experiment, for example,

One hundred ninety-eight U.S. residents were recruited using Amazon’s Mechanical Turk and participated in return for a small payment. Participants were 52% male and 48% female, with an average age of 33.3 years. Participants’ reported political affiliations were 40% Democrat, 20% Republican, 36% independent, and 4% other.

In this study

...we asked participants to rate how well they understand six political policies. After participants judged their understanding of each issue, we asked them to explain how two of the policies work and then to rerate their level of understanding. We expected that asking participants to explain the mechanisms underlying the policies would expose the illusion of explanatory depth and lead to lower ratings of understanding….

This is the result obtained (motivated readers can obtain a PDF of the article with details from me).
The second study:

..was to examine whether the attitude-moderation effect observed in Experiment 1 was driven specifically by an attempt to explain mechanisms or merely by deeper engagement and consideration of the policies. To induce some participants to deliberate without explaining mechanisms, we asked one group to enumerate reasons why they held the policy attitude they did. Listing reasons why one supports or opposes a policy does not necessarily entail explaining how that policy works; for instance, a reason can appeal to a rule, a value, or a feeling…we predicted that asking people to list reasons for their attitudes would lead to less attitude moderation than would asking them to articulate mechanisms.

The third experiment

...examined whether the moderating effect of mechanistic explanations on political attitudes demonstrated in Experiments 1 and 2 would extend to political decisions. As in Experiment 2, participants first rated their position on a given policy and then provided either a mechanistic explanation of it or reasons why they supported or opposed it. Next, they chose whether or not to donate a bonus payment to a relevant advocacy group. We predicted that participants’ initial level of support for the policy would be more weakly associated with their subsequent likelihood of donating in the mechanism condition than in the reasons condition because articulating mechanisms attenuates attitude extremity more than does listing reasons.