I am not sure I agree he can’t sue. Sure, sexual orientation might not be clearly federally protected. However, the teacher is the one that was fired. I have to think he has an employment contract and I doubt this violates the contract. A person in recovery from drug abuse or a lawyer stripped of his law license telling their stories of struggle would not violate the rule I bet. Those aren’t protected classes either. It is the teacher who is owed due process not the speaker.