Law schools perform four primary tasks, two of which they recognize, and two of which remain for the most part repressed or denied. The two recognized tasks are edification and vocational training. The two repressed functions of law school are social sorting and ideological legitimation.
From a comparative law perspective, the legal professionalization process in the United States is almost unique in that in the vast majority of cases it requires people to experience, or at least purchase, seven years of higher education. Even if we limit our perspective to the Anglo-American common law system, it's important to note this is a very recent development (for 90% of that history the Anglo-American legal world got along without anything resembling this requirement). The key question about the modern American law school is, what exactly is it doing or supposed to be doing that justifies a requirement that is so extraordinary in both cross-cultural and cross-historical terms? To reply "preparing law students to become lawyers" is a banal generality that tells us nothing useful. How are we preparing law students to become lawyers, and why are we doing it in this way or ways?
For complicated historical reasons, the vast majority of ABA-accredited law schools (since the need to graduate from an ABA-accredited law school creates a barrier to entry to the legal profession almost everywhere in the USA I'm going to limit the discussion to such schools for now) are units of research universities, while the relatively few that are not are as a practical matter required to imitate the rest. Because we've become so accustomed to it, it's easy to overlook that the single most crucial aspect, from an economic perspective, of the ABA accreditation regime is that it requires these units to be post-graduate schools, meaning of course that law students must acquire undergraduate degrees before beginning their formal legal education. Given what actually goes on in law schools, this requirement ought to be treated as puzzling and problematic, rather than, as is typically the case, self-evidently desirable.
Very little of what goes on in law schools seems to have any direct relation whatsoever to the task of teaching somebody how to do the things lawyers do. Law schools don't teach people how to practice law, except by what appears to be accident ("[Law] schools teach skills in isolation from actual lawyering experience. 'Legal reasoning' is sharply distinguished from law practice, and one learns nothing about practice. This procedure disables students from any future role but that of an apprentice in a law firm organized in the same manner as a law school, with older lawyers controlling the content and pace of depoliticized craft-training in a setting of intense competition and no feedback." Duncan Kennedy wrote this in 1981, and with some marginal exceptions it remains true thirty years later).
Since law schools don't engage in anything that looks much like vocational training, and since they're either parts of research universities or imitating schools that are, the natural default justification for requiring three years of postgraduate education before someone can become licensed to practice law is that law school is at bottom an extension of the student's previous university experience. Law schools have ended up embracing that justification, although in a somewhat ambivalent and conflicted way.
The traditional rationale for the current structure of American legal education is that it imparted a special and rather mysterious set of intellectual (as opposed to narrowly practical) skills, known as "thinking like a lawyer." The idea was that mastering the science -- and it was originally conceptualized by Langdell, the founder of the case method, as a science -- of doctrinal case analysis would mold the mind of the adept from its original mushy state into a kind of ruthless steel trap, capable of impressive feats of rigorous logical deduction and categorical distinction, and thus enable the successful student to extract true and correct statements of what the law required out of what to the uninitiated appeared to be a mass of chaotic and contradictory materials.
The Langdellian model of legal education provided law schools in general and law professors in particular with such a flattering account of what they were doing -- law was conceptualized as the correct judgment regarding what judges said about what the law was, and law professors appointed themselves the judges of the judges -- that to this day it still dominates American law schools, both in terms of pedagogy and, more important, in regard to an implicit jurisprudential vision of what "the law" actually consists of. When American law professors talk about "the law," they're usually talking about the legal doctrines promulgated by appellate courts (indeed they almost always mean federal appellate courts, and usually the Supreme Court.)
The Langdellian vision of what "the law" is has, however, a distinct disadvantage from the perspective of the larger university, which is that it's almost complete nonsense. Indeed this awkward fact was noted within just a few years of its institutional triumph: The single most famous law review article ever written, Holmes's The Path of the Law, is essentially a 20-page demolition of everything Langdell believed. In the 112 years since, Langdellian doctrinalism has been declared dead countless times, by sociological jurisprudence, legal realism, law and economics, critical legal studies, post-critical realism, post-real criticism, and the thousand and one flavors of "law and." On one level nobody believes in Langdellianism any more ("we are all realists now") and on another level nothing has changed: legal education in America consists largely of purporting to extract True Propositions of Law from the rigorous analysis of appellate court doctrine (this is what law professors still mean, to the extent they mean anything at all, when they ask their confused and bemused students whether a case has been "correctly decided.").
Nevertheless. The intellectual absurdity of the Langellian vision also gave birth to, and continues to sustain, the endless critiques of it within the law school. The thousand and one varieties of "law and" are all at bottom attempts to at their most ambitious (realism in the 1930s, critical legal studies in the 1970s) supplant, and more often supplement or ameliorate, Langell's vision of law with something more academically respectable. And these attempts have certainly borne much fruit. A good amount of serious academic work has been done in law schools over the past few decades in particular, and this at times has had good effects in the classroom as well, assuming (and this is an enormously important assumption) that it makes sense for law school to be a three-year continuation of liberal arts education.
Unfortunately, it doesn't make sense. The problem with "law and" is not primarily that much so-called "interdisciplinary" or "theoretical" or "impractical" -- as if three years of doctrinal case analysis were practical! -- scholarship is bad. The problem is that, given what has become the economic structure of contemporary legal education, it is at bottom an exercise in self-indulgence on the part of the faculty who engage in it (who would be getting paid half or one third as much to do the same thing in other parts of the university, assuming they could get hired to do so). The vast majority of law students are in no way interested in paying $150,000 for a three-year continuation of their liberal arts education. They didn't go to law school because they wanted to go to graduate school to study law. They went to law school (leaving aside those who are killing time because they have no real idea what they want to do) because they were presented with a barrier to entry to the practice of law that required them to go to school for three more years, period, full stop.
I should make it clear that I'm a big believer in the value of liberal education. I believe that a reasonably well educated citizenry is far preferable to an ignorant and credulous one. I believe in learning for its own sake. I believe the children are our future. That said, there's no justification for forcing people to have seven years of post-secondary liberal education rather than four as a precondition to becoming licensed to practice law.
If the justification for the current structure of legal education in America is intellectual rather than vocational, then that justification fails for two reasons. It fails because all the traditional rigamarole about how we teach our students to "think like lawyers" is wildly overblown. There is a certain value to teaching somebody the basics of doctrinal case analysis, especially if, like approximately .1% of attorneys, that person is going to spend a lot of time arguing or deciding appellate court cases -- but this can be accomplished in three months not three years. There is a great deal of value to engaging in the serious study of law as a graduate school subject, or series of subjects, but the idea that in the United States right now 150,000 people should at any given time be in the equivalent of Legal Graduate School is obviously insane on its face.
Forcing people to spend $100,000 or $150,000, or $200,000 to learn the basics of doctrinal case analysis, or to engage in a three-year graduate school experience (or, as is the case at most law schools today, to endure a half-baked combination of these two largely contradictory educational programs) is, under current economic and social conditions, less justifiable than ever.