My current hypothesis is that they are lacking in two areas, Theory of mind and Ambiguity tolerance.
Animal studies have shown that people have mirror neurons that make it very difficult for people to distinguish between their perceptions and experiences. As a result, people have a very hard time avoid coming to faulty conclusions about the motives of others, as they confuse their own mental processes with those of others.
I have noted below about how most people so easily jump to a guilty conclusion. Jurors are told to withhold judgment until they see all of the evidence, but they just cannot do it. Likewise, most people cannot undo their first impressions. I now believe that the problem is rooted in a low tolerance for ambiguity.
I would call these two under-studied psychological disorders, except that most people are afflicted. Maybe there are studies on this, but psychologists have these problems themselves, so I am not sure I trust them.
It seems to me that these disorders might correlate with political beliefs. Liberals have the mindreading disorder and conservatives have the ambiguity intolerance. They both jump to faulty conclusions, but maybe for different reasons.
A recent study claimed a correlation between certain disorders and college majors:
Our results suggest that shared genetic (and perhaps environmental) factors may both predispose for heritable neuropsychiatric disorders and influence the development of intellectual interests.For example, relatives of bipolar depressed drug addicts were more likely to major in humanities than science. This is not exactly the sort of study I am looking for, but it is similar.