From a reader:

I guess the thing about tenure is this: Most critics say it protects bad teachers. In essence it is just the opposite. It protects good, excellent teachers from “helicopter parents” and personality conflicts with administrators. Say you are a clerk in a store, and a customer accuses you of being dishonest In your dealings with them. The accusation is not at all true. Do you think you should be fired? This happens quite often to teachers. Tenure is to make sure proper procedures are followed to make sure accusations are true/false. I am not saying what is said is always false, but there are 2 sides to every story. I was once accused of something I did not do, and there were 5 adult school employees present who were witnesses for me. There were even students who volunteered to come forward with the truth. I was lucky that I had school administrators who were willing to get to the bottom of the situation by a fair investigation, but all teachers are not that lucky. You might also have to deal with school board members who have a personal vendetta (this is especially true for those who are teacher/coaches) or want someone let go because they gave a daughter, son, wife,etc. that they would like to give that position to. Tenure is also needed in these situations.