Many subjects cannot really be learned from books. Regardless of how many history books you may read, for example, it will not shed the same insight as a profound discussion with a highly-experienced academic in the field. This is true for many aspects of the humanities.
Which isn't to say self-study is worthless, but rather that it is a poor substitute for interaction with your professors. IMHO to claim that liberal arts can be just as well studied by oneself is myopic and tunnel-visioned, and about equivalent to me claiming that aspiring nuclear engineers should pick up some textbooks instead of going to school.
IMHO the whole topic of the monetary worth of schooling is an interesting and worthwhile one - but discussions on it on forums such as this one is invariably tainted by the fact that many people in our field have incredibly arrogant and misguided superiority complexes about technical degrees over the arts. I personally tend to think that one ought to be responsible for their own academic spending, and that studies of the arts is a luxury that not everyone can afford - but I hesitate to voice this often, since many of my engineering peers hold this opinion out of disdain and trivialization of the humanities, and I really don't want to be associated with that kind of ignorance.
My undergrad humanities courses were 100+ students packed into a giant lecture hall listening to a professor talk. There was essentially no interaction.
That's the trick with the humanities - they are not hard sciences, there is no canonical body of knowledge to be passed on; This isn't a straight download. Many things are a matter of perspective, of experience, and of particular schools of thoughts - all of the above poorly communicated via mere books.
That's the difference between a history book vs. a good history professor. Even without the (invaluable) ability to interact directly, it's the difference between a dry recounting of facts vs. more profound linkages into other areas of the field, or entirely other fields of study altogether. Sure, by reading books you will make some of these connections yourself, but it's hardly as good as what you'd get in classes.
That being said, there are certainly bad profs who do just do the dry recounting of facts, in which case you are basically better off reading the textbook at home. The presence of these should in no way discount the enormous positive influence of college educations done right.
Also, if you're really interested in a subject, talking with an expert is fun. You're really missing out on the good stuff if you keep to yourself and your books. I think this goes equally for the arts and the sciences.
Many of my friends who didn't go to college (or commuted to college) held on to whichever high school friends also stayed behind. They didn't meet many new people or do many new things. While it's theoretically possible to seek out the same level of novelty and excitement college gives you, it's also hard enough that most people won't do it.
ps, i agree with you, and i didn't pay for most of mine.