Over at the Marginal Revolution blog (here), Tyler Cowen has an interesting post about the debates over whether tenure in higher education should be abolished. The chief purpose and value of his post is in identifying the important issues that tenure-reform advocates have so far failed to address. He takes something of a beating from the anti-academic crowd in the comments, but I (another pointy-headed academic) think he's generally right.
That said, Tyler neglects the original purpose of tenure, which is to protect academics who promote unpopular ideas against retaliation. Many of the commentators who oppose tenure seem to do so because they disagree with the (often presumed) politics of certain professors or, more broadly, the professoriate. If most academics agreed with Glenn Beck, my guess is that tenure would not presently be a political issue (or, perhaps, it would become a political issue for the left). But this is precisely why the original purpose of tenure remains important.
I would also point out that the abolishing tenure could have very different consequences in professional schools than, say, the liberal arts simply because the opportunity costs tend to be much higher for those who choose to become professors of law, medicine, business, etc. Most professors in those fields could earn far higher wages outside of academia; the same is not obviously true for English or Philosophy professors (much as I personally admire them). If the cost of tenure abolition for professional school academics were not offset, e.g., by increased wages, the average quality of that professoriate is likely to decline. No doubt those who blithely dismiss the value of higher education won't care about that, but the social costs resulting from lower levels of human-capital development could be significant.
Finally, tenure does seem to be declining in the academic marketplace. According to a recent piece in the New York Times (here), 57% of college professors had tenure or were on the tenure-track in 1975. As of 2007, that number had fallen to 31%. An ever-increasing number of students are being taught by part-time adjuncts. Whether or not this trend is good for society should be front and center in debates over tenure.