I see no reason teacher’s jobs should be more protected than anyone else. If you do a poor job, you should be out of there.
And as far as parents forcing an unfair firing – I’m sure it has happened, but I doubt it has happened often. During my entire education and my kid’s education, I can’t think of a single parent uprising for or against a teacher.
And normal employment law will protect teachers in those cases – just like normal employment law protects other professions.