In an essay at The New Yorker, Louis Menand recounts an episode from early in his career as a professor in which a student asked him, "Why did we have to buy this book?" Continuing in the student's mercantile language, Menand avers that the student was "asking me to justify the return on investment in a college education. I just had never been called upon to think about this before. It wasn’t part of my training. We took the value of the business we were in for granted."
Menand proposes three possible answers to the student's question. The first simply asserts that "you’re in college, and these are the kinds of books that people in college read." The second assures the student “You’re reading these books because they teach you things about the world and yourself that, if you do not learn them in college, you are unlikely to learn anywhere else.” The most baldly utilitarian response has it that "advanced economies demand specialized knowledge and skills, and, since high school is aimed at the general learner, college is where people can be taught what they need in order to enter a vocation."
The third answer is the one now implicitly given by the school as part of the state apparatus, and Menand expresses the usual dismay at the pass to which we have come when this is the primary justification for reading books in college (although he does also acknowledge that the situation isn't likely to change). However, I can't see that the other two answers are any better. The first would be true if this were 1935 and all college students were undergraduates at Yale, but it hardly describes the situation we’re in now. The second, which is Menand's own preferred answer, spells out perhaps the underlying justification for answer one, but if college students are no longer interested in learning "things about the world and yourself" in return for their "investment" in college (which in my experience they indeed are not, to the extent they ever were), this answer is no more compelling than the first.
The problem with all three answers, ultimately, is that they tie the value of reading a book (I'm assuming Menand has in mind primarily works of literature, since he's an English professor) to its potential value to the institution of college, to the school (most charitably, to the goals of "education"). In my opinion, a better answer would be something like this: "You should read that book because it's a significant book of its kind, one that anyone studying _____ ought to read." In my opinion, a literature professor's first allegiance is to literature, or to the period/genre/national literature the course covers, and as long as the college where the professor is employed requires or encourages its students to take courses in literature, this answer should suffice. All questions concerning the place of literature in a college curriculum need to be answered by administrators or campus committees, not by the individual professor otherwise just doing his/her job.
Perhaps the time has come to reconsider the literature requirement, however. Most of the justifications that need to be made of reading assignments occur in courses in which the majority of students would not be there if taking such a course were not a degree requirement in "general education." Although generally speaking I think it a good idea for as many people as possible to read as many worthwhile books as possible, I'm pretty sure that materializing this broad aspiration into specific college course requirements has not worked out that well. It has especially not worked out well for literature. Courses in "Introduction to Literature" or "American Literature, Beginnings to the Present" are hopelessly incapable of fulfilling the aspiration, at best providing some students with some "information" about the subject they might later be able to recall, at worst making most students resentful of being compelled to take the course and less likely to follow up on the assigned reading with voluntary reading of their own. Given the career and personal goals of most of the students who take such courses, there really isn't a good answer for them to the question posed by Menand's student. Frankly, I don't see why these students should have to buy the books to take this sort of course, and I don't really want to teach them.
Students who take literature courses voluntarily, or choose to major in English, Comparative Literature, etc., are implicitly agreeing to accept the instructor's judgment about what books are appropriate for them to read. They would have cause for complaint only if it were determined the instructor's judgment is demonstrably faulty or if the instructor is a demonstrably bad teacher of the subject. An instructor (not just in literature) should be asked to know his/her subject well and to present it with integrity. He/she should not be asked to justify the entire project of higher education as it currently stands.
Of course, a great deal of instruction in "literature," particularly in the bigger universities and more prestigious liberal arts colleges (as opposed to, say, community colleges and many "regional" universities) is no longer instruction in literature. Literature is instead used to indeed "teach you things about the world" through cultural studies or to improve "thinking" through critical theory. Perhaps this development over the past twenty-five years or so has managed to keep what are still labeled as literature courses in the curriculum, but soon enough the question "why did we have to buy this book?" will be a question about some theorist's magnum opus, not Melville. At that point, the utilitarian answer may actually be the most truthful one.