Carefully cultivated discourse is still abundant on HN, which is why I read this site regularly. They just aren't usually found under threads that touch non-strictly tech things like geopolitics, history, natural sciences, or lifestyle. Although I do agree the moderation needs to be more responsive in some of these situations, I have made peace with the fact that HN doesn't have 100% high quality discussion.
I wonder if in 100 years from now society will make fun of "carefully cultivated discourse" the way we make fun of the aristocrats who drink tea with their pinky out to show how refined they were.