Does academic tenure really protect radical thought? Does it create barriers for employment? There are two good blog posts about the downsides of giving professors a job for life.

Megan McArdle writes,

Most scholars in their sixties are not producing path-breaking new
research, but they are precisely the people that tenure protects. 
Scholars in their twenties and thirties, on the other hand, have no
academic freedom at all.  Indeed, because tenure raises the stakes so
high, the vetting of future employees is much more careful–and the
candidates, who know this, are almost certainly more careful than they
would be if they were on more ordinary employment contracts.  As a
result, the process of getting a degree, getting a job, and getting
tenure has stretched out to cover one's whole youth. So tenure makes
young scholars–the kind most likely to attack a dominant
paradigm–probably more careful than they would be under more normal
employment process.

Dean Dad questions the usefulness of tenure from an administrator's point of view. He talks about the enormous costs of supporting tenured faculty.

The cost of tenure goes far beyond the salary of the tenured. It
includes the opportunity cost of more productive uses that had to be
skipped to pay for a decision made decades earlier in a different
context. (We actually have people for whom staff jobs were created when
their tenured speciality went away. That’s a direct cost of tenure.)
It also includes the cost of the various bribes that have to be paid to
the tenured to get them to step up to acknowledge institutional needs:
course releases (a direct cause of adjunct hiring), preferential
scheduling (whether it makes sense for students or not), and even cash
stipends (which have to be paid for somehow). 

It's liberating to be done with academia (well, I'm 90 percent sure that I'm done). I'm going to APSA this year, but it's mostly as a tourist. The word on the street is that academia's employment woes should continue for the next few years. I'm moving on. So, I can freely say that these guys speak the truth.

The only positive aspect of the tenure system is the relief on my friends' faces once they get tenure. Grad school and the tenure process is grueling and unstable. People put off buying homes and starting families. Tenure marks an end of torture and the beginning of a normal life that other people enjoy in their 20's. I worry that without tenure, the hazing from peers would continue forever.