How much professors work may be an issue, but it can’t explain the rise in college costs. Professors’ salaries have barely risen faster than inflation for the last 30 years while college costs have risen much faster than inflation. Professors’ workloads have actually increased at most institutions over the same time period, and sabbaticals were always part of the faculty system, so that is not increasing costs. In fact, the proportion of full-time faculty at most colleges has decreased as the schools have hired cheaper part-time faculty to teach many classes. So, if you are looking for the greater-than-inflation increases in cost it makes no sense to look at faculty labor costs (see the AAUP website for all the stats.)
Love that approach. Eliminate the philosophical issue as irrelevant to stick to pure, provable facts. (typos corrected, and hat tip to More or Less Bunk for the main article, on professors getting paid too much).