I just remembered an incident from when I was in high school. One of the most popular teachers wore a black armband to school to protest the War in Vietnam. He was threatened with being fired. (We were in a school with a lot of military families. The kids had dads serving in Vietnam). I think he backed down because he did keep his job. I don’t think there would have been an issue if he had marched in a protest or written an editorial against the war.
We still do have free speech in this country, I hope. As a government employee a teacher has more free speech rights than a private employee who can be fired at will. Recently the Washington Post had a story about a woman who was employed by a government contractor who on her free time, while riding her bike, gave the middle finger to the presidential motorcade and was fired. She is arguing her free speech rights were violated.
I don’t know the answer but I do think there is or should be freedom for a teacher to voice her opinions outside the classroom. However, inside the classroom, students, who are a captive audience should not be subjected to a teacher’s political or religious viewpoints no matter what they are. Because any POV is likely to offend somebody. Stick to the lesson plan, teachers.