That's exactly my point. Why would someone downvote because he finds an opinion controversial? Offensive, unrelevant, I can understand. Unpopular, controversial? That's pretty much how echo chambers are made. Is omeone wants to hear the same opinion fot the rest of his life, then he can write it in google calendar and send it as notification every day. No point in going in a public space and trolling.

Because it’s against the rules of the website

"Eschew flamebait. Don't introduce flamewar topics unless you have something genuinely new to say. Avoid unrelated controversies and generic tangents.

Please don't post shallow dismissals, especially of other people's work. A good critical comment teaches us something."

It specifically says to make critical comments and to avoid only unrelated controversy.