I think this is an interesting topic too. Some ideas I've had on this:
You prevent people from posting terribly toxic comments in the first place, whether that's automatic moderation or warning them that their comment is toxic and to reconsider what they're about to post. I'm gonna plug http://www.getspectrum.io here b/c it's relevant.
Require answering a question related to the topic at hand before allowing comment submissions. I read about this being done by a news site in Europe not too long ago.
Prompt the audience/community with a specific question/prompt that the discussion/comments will be in about. That way every comment is a direct response to the same question. This could help keep things on topic. I think a lot of toxic comments are often from indirect tangents.
What if you could see comments that have been posted only after posting one of your own? That way your primary contribution is an organic thought and not an angered response to what someone else has said.