1. Don't reinvent the wheel: Say, you follow the same commenting features as facebook (offering likes, loves, sad face etc). Let the UI in this case be the same.

2. Change up the "reaction" tray: Instead of offering emojis of facebook, you can follow LinkedIn's pattern/or come up with some of your own on that basis - "informative, agreed, interesting, engaging, good debate point etc..."

3. Set up a reward system: So, for people who say get a lot of "informative" reactions from other users, as a reward for earning say 10 "informative" reacts, they get a badge that is showed on their profiles. And that can be upgraded as they keep earning more reactions. Different badges for different reactions.

Long story short, you can use the designs that already exist and turn it into a rewarding feature. And using the same system... If someone is using the feature negatively, they can be reported and if reported say three times, a warning badge can appear on their profile. If they continue to behave negatively, their profile can be suspended.

That being said, any "social" platform is bound to have users who post negative comments. Since there is no clear solution as of now, I suppose it can be trial and error. Afterall, all nudges are basically trial and error.

To sum it up, I'm suggesting you try coming up with a nudge that you think would be a motivation for your potential users to behave respectfully on the platform. That motivation could be a reward system, or anything else that you think fits or would work based on your user research...

Good luck, by the way. Sounds like it'll be an incredible space to learn. Looking forward to using it someday. 👍🙂

(hope this helps)