I don't know where you get your information, but this is DEAD WRONG in my state!
I am a tenured teacher in MO. I can tell you that I can be fired at any time. The ONLY thing tenure does is give me due process. If I am not an effective teacher anymore, all my administrator needs to do is meet with me.....tell me the areas that are lacking....and give me an opportunity to correct it. If I don't, they can let me go.
One of the men I teach with (who is a fantastic teacher, BTW) questioned one of our administrators about an issue he thought was unfair. He was very much in danger of being fired. As a matter of fact, he would have been fired....but, he had to agree to read a book on effective communication strategies, and he had to meet with me (I was to act as a mentor and go-between) to discuss the book.
I agree....many teachers in the profession are in it because they don't know what else to do. Many teachers, especially later in their careers, check out. These teachers need to be replaced. But, don't blame the teachers. If you have effective administrators, then bad teachers aren't hired year after year. Bad teachers are replaced, or receive training to help them improve.
Most teachers I work with are in the profession because they love kids (nothing is more rewarding than to see the "Now, I get it" look!), they love their content area (history is my PASSION), or they want to make a difference. Actually, most of us are in it for all three reasons.
I honestly don't know what kind of education you had....but for you to have such a negative view of teachers it must have been pretty bad. Rest assured there are still many of us that love the profession, love the students, and love our communities!