tenure, as far as i'm concerned has an ethical-political justification: the free speech, knowledge issue. QED! :)
i think the claim that we are only able to do certain kinds of work is a myth -- surely not objectively true. annalee newitz wrote a piece about how the structure of the PhD career is such that it tends to make you think that academia is ALL that you'll ever do. Out of Academia Why do we think that PhD's are only good for making someone into a professor? By Annalee Newitz, from Salon.com http://www.salon.com/it/career/1998/11/06career.html