One thesis I particularly like takes off from George Marsden, "The Soul of the American University: From Protestant Establishment to Established Nonbelief". The idea is that ever since Harvard was founded, academia has been more liberal than the society at large. Most private colleges (like Dartmouth and Carleton College) were founded in connection with a Protestant denomination, but Marsden shows the tendency has been for them to evolve into secular (liberal) institutions. If I remember him correctly, the reason is one beloved of conservatives: competition.
To get students, and financial support, colleges had to reach further than their founding denomination and initial area. By competing over a wider space, both geographically and intellectually, they spread their fixed costs and increased their stability. Broader appeals meant minimizing theological correctness and ideology and emphasizing science, rationality, achievement, equality, democracy (the good liberal universalist virtues), as well as football teams and academic stars. The universities Marsden studies became secularized in the process, which undermined a foundation stone of conservatism. (He ends with the Bill Buckley's "God and Man at Yale" controversy in the 1950's.) It looks to me as if there was an educational establishment by 1950. Carnegie had seen to it that professors had a national retirement plan , the professional organizations were dug in, the AAUP was fighting back against McCarthyism, Harvard and Yale were the leaders and pacesetters, and ETS started pushing SAT.
(I don't know if this qualifies as "horizontal competition" in economics, but see Achenblog for a neat piece on it. The point is that competition forces the competitors to become more like each other, whether in location or in facilities and character. As of 1950 the Big Three carmakers each sported a full line of models, and the Kaiser-Frasers, Studebakers, and Nashes of the world faded away. The Big Three networks all had news departments and were very similar in content. I suspect all the elite colleges cover the same fields of study with few differences.)
Certainly when I went to college in 1959 many people on the right thought there was a liberal/pinko/egghead dominance of college faculties. Academia (faculty) was dominated by WASP males and some Jews. As for the student body, the colleges I applied to talked about diversity, but they mostly meant geographical. I think I remember 3 blacks in a class of 800. Males were a majority. Today my alma mater is 50/50 in sex, 27 percent minority, probably most Asian. In my field of history a popular theory was "consensus history"--the idea that America was always a liberal middle class society, lacking the hereditary upper class and the proletariat found in Europe.
I've not been back to college since I busted out of grad school in 1965. I have tried to keep up, through the Alumni mag and my history journals.
So, if academia was liberal in 1965, what would have kept it so?
- Discipleship--seems to me that professors have "their" grad students, whom they try to place. That would tend to perpetuate any liberal bias.
- Culture--I think all organizations have a culture that gets perpetuated through the air.
- The appeal of the new--in the competition among grad students for places, topics that are new are favored over the old. (See labor history and agricultural history for two fields of declining importance in history, even though both would tend "liberal".)
- New demography--colleges started going after new groups, notably blacks, but also other minorities and women. This is true both in the student body and in the faculty. It so happens that the new demographic groups are also the most liberal in the general population. In the case of women, they seem to have gone most strongly into fields that are now most heavily liberal (i.e., English and the arts, then social sciences).
- Stronger competition--look at the attention paid to the US News ratings. Colleges are much more selective these days. One of the big criteria is selectivity. That's in line with the rule in literature: the more dead bodies the hero steps over, the greater the reward at the end of his quest. So every college in the competition wants to maximize the number of applicants. I might be cynical and say that the purpose of affirmative action is, in part, to attract more applicants to be rejected, which thereby increases the selectivity of the institution. But having a diverse professoriate, having people on the faculty with whom a possible applicant can identify, thus becomes very important. (See the LA Times article on celebrity instructors.)
- Conservatism is not important among the incoming students. For the majority of students, college is probably a rite of passage and a ticket to punch (just as it was in my day) so the college's prestige is important, as are extracurricular aspects. (Liberalism isn't important to most, but having female or black role models will matter to some.)
- Disdain for other occupations. It's true that people tend to demonize the others. So all things being equal, one should expect academics to denigrate those in business or government. They've been doing that since time immemorial, and seeing it done to them. (Those who can, do; those who can't, teach.)
- Liberal guilt--one of the downsides of the bleeding heart liberal is that we become guilty very easy. That meant, and may be still means, that liberals will favor those who have no power, who have been oppressed.