Thank you for sharing your story. I hope many people get a chance to read it.
Tenure is very important. It is a right that teachers have fought for and sacrificed for and earned. The idea that there are so many "bad" teachers is ludicrous! For most people, "bad" teacher means:
Didn't give my special snowflake an A++++
Didn't put up with my snowflake's bad behavior
Gave snowflake too much homework
Hasn't brought snowflake's grade level up 4 years to be equal to his peers
Has 35+ special snowflakes in her class and must give special attention to all of them
Has an administration that does not support the teacher in the classroom, including discipline
In the schools that I attended, in which my mother taught for 41 years, and during my short stint in teaching, I can think of two teachers who were incompetent. One of them was a math teacher I had in high school. And you know what? I wasn't ruined or traumatized. If a teacher does something illegal or inappropriate, they are fired. This is just propaganda to bust the teacher's unions and privatize schools.
Support Teachers!