I ask this with the greatest amount of respect: Is it possible that you're taking that "mission statement" a little too seriously here?
I'm a casual HN user and I open the front page 3-4 times per day. Roughly 50% of the topics tend to be well-written but ultimately standard blog posts from random technologists on fairly standard technology topics.
Some of it is indeed interesting, and what's interesting of course depends on the reader, but I think it's safe to say that most people won't open the front page and be utterly blown away by how incredibly interesting every single post is.
Considering this, silencing a lively discussion because it might not meet certain, ultimately subjective, criteria of "interestingness" seems excessive. To be clear, I don't want to see the front page dominated by a single topic every day, but it pains me when discussions containing (among other things) thoughtful comments are effectively hidden from view in a matter of minutes because an algorithm or a moderator thinks we'd be better off reading about how someone has connected their dog's heart rate monitor to their car's entertainment system using a Raspberry Pi.
Don't get me wrong: I'm not saying it is interesting. There are all too many ways in which it is not. I just mean that that's what what want it to be, and try to help it be. Even though we fall short.
Connecting a heart rate monitor to a car does sound kind of interesting to me though! but not with a dog - that sounds too close to abusive. But I could imagine someone making a biofeedback system where their heart drives their car or something. That would ba a great HN post.
And, ironically, even interestingness can get repetitive. When I see a post titled "How I made Netflix' video decoding on Android 25% faster", I know that I'm going to find a war story where some silly hardware bug was preventing proper cache management or something. It's interesting in a way, and if I read the full post I'm going to learn plenty of new things – but at the end of the day, I've seen (and done) it all before. Not this particular bug of course, but this type of story.
What I'm really looking for is ideas and thoughts that are completely new to me. Not just in their particulars, but in their general direction. That's very difficult to find. And "dissenting", "controversial", and "offensive" opinions are an absolutely crucial part of finding it, in my experience. A "sort by controversial" feature like Reddit has would be a godsend for HN.