I would think you might have grounds to complain. I would not have ever done that when I taught biology. And I didn’t give my opinion on the topic, just taught the material. Of course the kids are free to discuss and express their opinions, but any time a teacher does, I would think they are at risk. Make sure that’s really what the teacher said and go talk to the principal. If you don’t get satisfaction, kick it up a level higher. BTW it would probably help if you got more parents involved. Believe me, principals don’t like mad parents.
My HS biology teacher opened the year with a statement that went something like this:
“In this class I teach the theory of evolution. For the purposes of this class, all test questions should be answered in accordance with this theory, as presented in class and the textbook. Your personal beliefs outside of this class do not have any bearing on the correct test answers.”
He was a christian, and a pretty good teacher.