My father is a retired teacher. My brother and his wife are teachers. My wife is a school counselor. All that said tenure is a crock of bull. Once they get it you can't hardly get rid of them. I believe they have to be hired back for year 5 to actually get it so the administration has failed if they are that bad and make it that far.
Tenure is not a teacher issue. It is an administration issue. I know in Alabama where I teach we work three years and then are granted tenure. We can be fired for any reason in that first three years and not given a reason. Some principal obviously did not do their job or they would have canned this person long before they gained tenure. With that being said it is not impossible to can a tenured teacher but the issue is so many admins want to not tackle the tough issues.