There could be a plugin for this. Imagine that before sending a post, you have to answer a few questions, such as: "Your certainty that this post will move the sanity waterline in a positive direction".
But we are only humans. We would learn very soon to ignore it, and just check the "right" answers automatically.
Maybe it would work better if it displayed only randomly, once in a few comments. And then the given comment could be sent to reviewers, who could inflict huge negative karma if they strongly disagree with the estimate.
Or perhaps there could be an option to click "I am sure this comment is useful and harmless" when sending a comment. A comment without this option gets +1 karma on upvote and -1 on downvote; a comment with this option gets +2 on upvote and -5 on downvote. This could make people think before posting.
But we are only humans. We would learn very soon to ignore it, and just check the "right" answers automatically.
There could be something preventing you from unthinkingly click "Yes", akin to the option in LeechBlock whereby you have to copy a code of 32/64/128 random characters before being able to change the settings. (But that might backfire, by discouraging people from posting comments even when they would be unobjectionable.)
...Or perhaps there could be an option to click "I am sure this comment is useful and harmless"
If it's worth saying, but not worth its own post, even in Discussion, it goes here.