Speaking as a retired teacher, I believe tenure is not some obsolete perk that good teachers ought to be willing to give up. Procedures already exist to remove incompetent teachers. Go ahead and toughen up the process, if necessary. But tenure remains essential because of the nature of the job.
Teaching is an unusual profession in that teachers must satisfy the needs of over a hundred students a day, plus the parents of those students, plus colleagues and administrators. Only in politics or Hollywood would a person at work face such daily scrutiny from so many directions. In addition, these observers have their own agendas. They are judging your style, intelligence and personality according to their preferences. Without tenure, teachers are at the mercy of a vindictive parent, an angry colleague or a controlling boss (and principals change schools frequently).
Teachers need protection from random disapproval that could unfairly end their careers.
George Johnson, Clayton