The reality is that most teachers take their jobs seriously. There are very few who get tenure and then try to do nothing. What many fail to understand is that tenured teachers are evaluated by their superiors multiple times throughout the school year. If the principal is worth their salary, they will get every teachers to perform. Simply put, principals have creative ways to make teachers life miserable if they dont comply. I dont know of ONE situation where a principal walked into a classroom filled with students and the teacher was doing nothing and told the principal "you cant do anything, I have tenure." I know that many of the teacher bashers want to think that but that is far from the truth.
Firemen, cops, sanitation workers all have tenure as well. They just dont call it tenure. They all have the same job protection with less waiting period (90 days) and FAR less education requirements.