Chris Beam makes the case for nixing tenure:

The most common pro-tenure argument is that it protects academic freedom. Once a professor gains tenure, the thinking goes, he or she can say anything without fear of being fired. Academia thrives on the circulation of dangerous ideas.

The problem is, for every tenured professor who's liberated at age 40 to speak his mind, there are dozens of junior professors terrified to say anything the least bit controversial, lest they lose their one shot at job security for life. Academia relies on young scholars to shake things up. Yet tenure incentivizes them not to. Instead, it rewards students who follow in the footsteps of the elders whose favor they will require when the day of judgment arrives.

McArdle and Poulos debated this topic a few weeks ago.