It helps prevent hivemind mentality and keeps us growing. Unpopular opinions often have ideas worth examining or could be outright correct despite common wisdom saying otherwise, and forums like these are one of the best places for us to engage with those facts. There's also times when an opinion we like dislike is misinformed, and rather than send it to the bottom, it's good to explain how it's wrong for both our own sake (refining our arguments) and bystanders that haven't given the topic much thought.

But if someone left a turd, send that stank to the bottom!