Its completely ok to have an opinion. It actually is pretty important. But teachers shouldn’t teach their opinion as the truth. I have to face this behavior everyday at my school in switzerland. As a proud libertarian, i was very shocked as my teacher showed the anticapitalist, enviromentalist movie called “tomorrow”. There were no discussions about the problematic points the movie made. It was taught as the truth. The only truth.
The tides turned, as i got to speak to a journalist, who was interviewing me about a political event, i went to. I described my problem and the whole thing got published. Of course it was shortened and the most important points were cut out, because they were probably to “aggressive” .
But then (after the article appeared in the newspaper) the leftist/socialist behavior of my teacher disappeared, meaning we stopped watching “tomorrow” and about all the future controversial subject, we held debates with the whole class.
The main point of my little essay is, that we don’t have to make non-neutral-teaching illegal, but expose them with newspapers and television. In switzerland, this works perfectly.