The internal culture of the military is something I don't fully understand. I haven't served, and the relationships seem so different from my day to day life that I don't really have an intuitive grasp on how things work. With that disclaimer in mind, from a policy perspective (leaving aside the constitutional issues for a moment) this rationale as expressed by Nathaniel Fick, a former Marine captain and author of a book on his war experiences, called One Bullet Away, has always seemed to make some sense to me:
Mr. Fick majored in classics at Dartmouth, and he speaks about being motivated to join the Marines by a talk given by Tom Ricks, a Washington Post reporter who covers the military. Fick says that Ricks was an advocate for ROTC on campus during his talk, and a professor challenged him, saying if you bring the military onto our campus you'll screw up our peaceful nature and tolerance.
Ricks replied, no, what will happen is that you will liberalize the military. You will influence the military and it will influence you.
I have only begun reading Fick's book, but I have seen him interviewed on tv, and he seems to agree with this claim (which is one of the reasons he starts his book with it, I think). It seems to me that this "liberalizing" effect on the military is even more valuable today, given the extensive civilian responsibilities that modern soldiers undertake. And the impressive performance of the JAG Corps in dealing with the Abu Ghraib fiasco is also suggestive of the influence that good people can have on the military.
As I said, I don't have any personal experience with whether this is an accurate claim, but it seems intuitively plausible to me. I would be interested in hearing from any readers out there who have served in the military as to whether you find the claim "You will influence the military and it will influence you" actually works out that way in practice, especially for those who serve as officers (presumably the relevant category for ROTC and JAG questions). I'm not so much interested in the constitutional questions here (which have been hashed over extensively here and elsewhere this week), but hearing personal experiences about the culture of the military and the opportunities that individuals may have to influence that culture.
Several of the Commenters raise the good point that it is not exactly clear what the term "liberalize" here means. My understanding is that those using the term (such as in Fick's story) do not intend it to mean politically or ideologically liberal (thus suggesting that the military is somehow reactionary in nature) but rather something more along the lines of what is meant in the term of "liberal education" or "liberal arts education." I think they have in mind someone who is the product of a broad and well-rounded education in the libearl arts & sciences in a predominantly civilian college or university. Tolerance, thoughtfulness, and independent thinking, is my impression of the virtues that are being sought here. At least that is what I have in mind when I think of the term in this context.
As one of the Comments puts it:
P.S. "Liberal" in this context is NOT describing a political viewpoint, but rather a "liberal" education, as one grounded in the liberal arts and sciences that teaches one to think, as opposed to say a vocational education, that teaches one to do a job.
A couple of interesting examples of the idea, such as Pershing and Caesar, are discussed here.