When I was in university, one of my History profs (Malcom Murfett) encouraged us to disagree with him: "If you disagree with me, have the guts and say so."
I carried this spirit to my teaching life and often echoed Prof Murfett's words, but not so aggressively.
I would say, "If you disagree, please tell me. You will not be punished for expressing your opinions." Even if the opinion is not in line with the school's policy, I think we should still hear out the kids.
There was one year when a student dissented with me in class. I had made the observation that just like Americans have guns, Singaporeans use their handphones as "weapons" (social media).
This student said, "Bad example!" and started booing.
This triggered me and I told the student that he is free to disagree and we can have a discussion. But if he started heckling me, what discussion could we have?
"This speaks volumes of your upbringing." I said. He must have not liked what I said because what little rapport we had built up evaporated after that.
I have no regrets, though.