Source: Stuart Hampton
Part of the explanation is the “Openness” personality trait, one of the big-five or big-six personality factors. People high on Openness get more pleasure from higher education and tend to seek it out. (Citation 1, below.)
Longitiudinal studies of personality such as the Baltimore Longitudinal Study of Aging show that higher education doesn’t have much effect on personality. The causation works the other way around. Open people are more likely to continue seeking education throughout their lives.
On the other hand, higher education is correlated with income. The average Democrat has a lower income than the average Republican. So, the relationship between education and liberal vs. conservative views is not so simple.
Citation 1: Friedman H, Schustack M (2016). Personality: Classic Theories and Modern Research (Sixth ed.). Pearson Education Inc. ISBN 978-0-205-99793-0.
Edit – 8 hours later. I should add that the big-five and big-six personality traits like Openness are stable over periods of decades at least, and probably over a lifetime. These traits develop during childhood and pretty much lock in during the teenage years. They are insensitive to big changes in circumstances. People get married, get divorced, get jobs, lose jobs, have children, or don’t, get more education or not, but their personality traits remain about the same. (On the average. There are some exceptions of course.) That’s why neither higher education nor exposure to “liberal values” at universities cause people to become more liberal. There is no simple explanation for why people from the same family can have very different personality traits. Openness, and the other four or five fundamental personality traits are partly inherited, but also emerge from unknown sources and influences during the first ten or fifteen years of life.
Another edit: There seems to be some interest on this thread about the Openness trait, so I’ll add this excerpt from the extensive Wikipedia article on Openness:
There are social and political implications to this personality trait. People who are highly open to experience tend to be liberal and tolerant of diversity. As a consequence, they are generally more open to different cultures and lifestyles. They are lower in ethnocentrism, right-wing authoritarianism, social dominance orientation, and prejudice. Openness has a stronger (negative) relationship with right-wing and left-wing authoritarianism than the other five-factor model traits (conscientiousness has a modest positive association, and the other traits have negligible associations). Openness has a somewhat smaller (negative) association with social dominance orientation than (low) agreeableness (the other traits have negligible associations). Openness has a stronger (negative) relationship with prejudice than the other five-factor model traits (agreeableness has a more modest negative association, and the other traits have negligible associations). However, right-wing authoritarianism and social dominance orientation are each more strongly (positively) associated with prejudice than openness or any of the other five-factor model traits. Recent research has argued that the relationship between openness and prejudice may be more complex, as the prejudice examined was prejudice against unconventional, low status groups (for example sexual and ethnic minorities) and that people who are high in openness can still be intolerant of those with conflicting world views.
Anothernother edit: This is probably also the explanation for the often-alleged “liberal bias” in journalism. People who choose journalism as a career are probably unusually curious and open-minded. Along with journalism, they often study sociology, government, psychology, literature and philosophy in college, before they become journalists. Many hope to publish a novel some day. Many famous novelists began their careers as journalists. Mark Twain, George Orwell, Doestoevsky, Truman Capote, Tom Wolfe, Hemingway, Jack London, and so on.
I would argue there is not much of a controversy or a debate around the fact that academics in America tend to be liberals. See for example the results of this Pew Research Center poll:
Highly educated adults – particularly those who have attended graduate school – are far more likely than those with less education to take predominantly liberal positions across a range of political values. And these differences have increased over the past two decades.
Gross’s book on the topic provides ample evidence to this point:
Together, radicals, progressives, and center-lefters make up the left/liberal flank of American academia. Looking at the numbers from the latent class analysis, this means that about 54% of American academics can be said to belong to the political left […] a reasonable conclusion is that between 50% and 60% of academics fall somewhere on the left side of the political spectrum.
There are of course variations, as in one can find more conservatives or strong conservatives in some fields:
Where in academe can moderates, libertarians, and strong conservatives be found? Again, the PAP data are not very helpful in identifying libertarians, but something can be said about moderates and the two right-leaning groupings that the latent class analysis turned up. Table 1.1 shows how all six of the clusters are distributed across types of institutions and broad disciplinary areas. Economic and strong conservatives are underrepresented at elite, PhD-granting institutions and liberal arts colleges; strong conservatives are underrepresented as well at nonelite, PhD granting schools and overrepresented in community colleges. In terms of disciplinary differences, economic and strong conservatives are overrepresented in business, and the former in engineering as well. A more fine-grained analysis shows that conservatives tend to cluster in fields like accounting, management information, marketing, and electrical engineering, while economics contains a higher proportion of strong conservatives than do social science fields such as sociology and psychology […]
In any case:
While many of these differences are interesting and worthy of explanation, the first finding from the interviews and the PAP survey that must be accounted for is simply that there is in fact a concentration in the academic ranks of people broadly on the left.