We may think we’re being scientists, but we’re actually being lawyers. Our ‘reasoning’ is a means to a predetermined end—winning our ‘case’—and is shot through with biases.
Basically when you ask questions where the left-wing answer is also the one supported by economics, suddenly left-wing people have a better understanding of economics. But when you ask the other set of questions, it comes out the other way. Basically, there’s a lot of confirmation bias out there.
Why Do We Overestimate Our Abilities?

A bunch of factors play a role, according to a new study:

"Subjects (1) place approximately full weight on their priors, but (2) are asymmetric, over-weighting positive feedback relative to negative, and (3) conservative, updating too little in response to both positive and negative signals. These biases are substantially less pronounced in a placebo experiment where ego is not at stake. We also find that (4) a substantial portion of subjects are averse to receiving information about their ability, and that (5) less confident subjects are causally more likely to be averse."

(hat tip: Robin Hanson)

Start with a faulty premise, add time and intention, and voilà! — without constant efforts to challenge our beliefs, the cognitive shortcuts and motivated reasonings we are all prone to can easily cement into impossible-to-dislodge conspiracy theories.
Social conservatives were more likely than others to misattribute responsibility for specific behaviors, but only when doing so resulted in a negative view of the minority group. This memory trick apparently resulted in false evidence building up in their minds, reinforcing their hostility.