It's good to look at both sides and be open minded, but I'd say if that is suppose to be taught, the teacher has an obligation to teach it or be replaced. Personal belief is wonderful, but there has to be some respect for the syllabus. What is someone has the personal belief that one race is superior to another. Are they justified in teaching that regardless of it not being in the syllabus. What if they disagree with certain historic events. Are they justified in skipping the teaching of them?

In a private academy, perhaps. But in a government funded school, standards must be followed.

(I say that as a vegan)