A very good read. Perhaps nothing groundbreaking, but very worthwhile to point out the actual state of things given both the political pieties mouthed on behalf of diversity, and given the very real implications for society and democracy of living in a hyperfragmented state.
The section on academia is a bit overstated, though, I can state from experience. There are plenty of conservative professors at Harvard. Yes, they are clustered into certain departments--of those disciplines where politics is relevant, in economics in particular, and many in history; and of those where it is not, quite a few in CS, engineering, chemistry, etc. Certainly particular departments have carved out individual cultural/political niches for themselves--Literature, for example, is quite a bit to the left of English, even though they cover essentially the same subject. On the other hand, there's still quite a bit of a range within each department; as an extreme example, I took a course from a quite staunch and quite politically active conservative (and, more to the point, anti-liberal) who teaches out of the Lit department.
There's no denying, of course, that the academy--in particular at the elite universities--drifts far left of the American mainstream, and even significantly left of the highly-educated as a whole. But I think this is less due to unconscious partisanship on hiring committees (as Brooks alleges) than to self-selection on the part of potential professors (which he also posits). But I don't think the root cause of that self-selection is due to conservatives not wanting to hang with a bunch of liberals. Rather, I think that many conservatives belong to the "those who can, do; those who can't, teach" school of thought; while many liberals are more of the opinion that "those who do, are heartless bastards who ruin things for the rest of us; so, might as well teach." A career in academia, particularly in the social sciences, just fits in better with a liberal outlook; but those conservatives who nonetheless feel like academic research and teaching do just fine, AFAICT.
In any case, all this focus on diversity in the professorial class misses the broader point of the social and political diversity experienced by the undergraduate students themselves. And on that point I was pretty pleasantly surprised by my Harvard experience. The fact of the matter is that there's a great deal of viewpoint diversity, and even of cultural diversity (although there's less of that); certainly much more than in any local slice of the real world. Harvard does tend to be extremely fragmented along those lines--when you take the country's 1650 kids with the "best" high school extracurriculars, you end up with a hell of a lot of useless proliferating student organizations--but it's a small enough place that all those islands of homogeneity end up overlapping into a reasonably diverse whole.
Of course radical left ideologies are quite overrepresented among students at elite colleges, although they're still fringe viewpoints. But IMO this is not so much because of any influence on the part of a liberal faculty, but rather because a) 18-22 is a fertile age for radical leftism, and b) it's moreover a fertile age for rebelling against/questioning the cultural assumptions of one's parents and the (as Brooks points out) quite specific neighborhoods, institutions etc. one grows up in. Those who make it into an elite college tend to have had the sort of cultural background against which radical leftism is an easy form of rebellion.
Meanwhile, I have to say by far the most surprising and perhaps even one of the most dominant cultural ideologies I found myself exposed to for the first time while at Harvard was...devout Christianity. Of all stripes. Even evangelical Christianity, to an IMO shocking degree. Plenty of Mormons too--and they meant it: they all either got married right out of school (or during school), or went on Mission, or fricking both in some cases. Of course these were mostly Christians who were more prone to an intellectual and philosophical theology, but they were in general no less devout or orthodox for it.
This is particularly ironic because of how I never ran into this sort of culture where I grew up--in St. Louis Missouri; not in the Bible Belt but not far from it either. The closest I've come to devout religiosity in St. Louis has been my good (mostly non-practicing Catholic) friend who believes a little too much in ghosts. This isn't, of course, because St. Louis as a whole isn't wildly Christian--it is. It's because the places I go in St. Louis--the people I know, the schools I went to and they went to, the Little League I was in, the people my parents know, the places I shop, the institutions I come into contact with from day to day--are all part of St. Louis's narrow Reform Jewish corridor--a geographic demographic feature that's probably only about 30% Jewish (as compared to maybe 4% for the metropolitan area as a whole), not overly liberal or hyperintellectual, and certainly not anti-religious or atheistic or even agnostic, but is just not given to earnest, devout, or public religiousness. As a cultural matter more than anything else.
In a way this is Brooks' point exactly--that even in red state religious middle America there are well-defined pockets where the attitude towards religion is frankly downright European. (Of course when I lived in Europe I spent most of my time in small-town Sicily which, believe me, is plenty religious.) That, more broadly, culture exists in fine-grained pockets so tightly cordoned off that one can grow up without even realizing the actual attitude of the wider culture around him on so basic a value as religion.
But as to his specific point about elite universities being another example of this lack of diversity: bunk. And as to his implied argument that we needn't really worry about ensuring diversity in universities when we accept so total a lack of true diversity in our later lives: couldn't be more wrong. Precisely because our later lives are so finely culturally calibrated--that's why universities have a duty to present a true diversity of culture and viewpoint; so that socially mobile students can be exposed to all of that and thus make an informed decision between SoHo and Fifth Ave. in later life.
He might not have intended to, but IMO Brooks makes a persuasive argument that the diversity rationale for affirmative action--so ridiculed among the right--is actually vitally important to the mission of an educational institution. That if anything it ought to be broadened from a sheer focus on ethnic background to encompass diversity of experience, class, talents, interests, geography, viewpoint, culture, etc. Except that--at least as far as the admissions practices of small selective colleges go--that's a straw man; all of those things are already taken into consideration in the admissions process.
Anyways, I'm rambling now.