These types can quickly dominate the threads. That repels the smarter people who have no interest in such threads. This is how HN could fall into a death spiral. Worse, the risk grows as the site grows, because then more people are attracted to it for wrong reasons. (Right reason: curiosity. Wrong reason: hearing the sound of one's own voice, or making others do it.)
I think the only way you could sustainably have a forum of the kind you describe would be to close it off from the public internet. We're not going to do that with Hacker News. This arguably does leave the site "a little flat"—I've made the same point in the past using the word bland instead of flat. But better flat than dead.
While it may be enticing to think of a flamewar as a crucible for good discussion, I think that it's far from the case. Fierce, passionate criticism is not the same thing as people talking past each other to attack straw men. There's little time or incentive to sift through the ashes looking for some purified argument that's withstood the flames when you can rush into the next thread in the forum where the a new fire is just getting started. This is pretty clear to see when the same ideological discussions are rewarmed again and again.
And battle is not how you get there.
I think HN has been a place for lively debate at times. Perhaps it shall be again.
I have this hypothesis that thinking is layered on top of our two primal emotional strategies for stress: connection and aggression become diffuse mode (how is it similar?) and focused mode (how is it different?). When i use the word “battle” I am suggesting repurposing aggression so that instead of directing it at each other in defense of our positions and ego (system 1 thinking) we are working together synergistically in a battle for the truth which will enable us to solve the problem (system 2 thinking).
i.e. Turning a zero sum game into a positive sum game.
Just because something is familiar doesn't mean it's not worth exploring. Often seemingly familiar things are misunderstood because we don't take the time to understand them.
> ...what things make the HN ecosystem more rich and complex vs. what things make it dumber...
I think "flamewar" avoidance leaves HN a little flat, actually. There is a lot rich and complex in giving the usual tech/SV crowd a challenge to its viewpoint from time to time. The goal isn't always changing minds or learning new things. Sometimes it's just to realize that smart people can disagree with us, and because of that, we need to respect people that disagree with us.
Maybe we need to let passionate, smart people have it out from time to time so everyone can be reminded which positions can stand up to the flames just fine. Otherwise, we forget that the farces of "them" that we enjoy are just farces, not reality. And that makes us dumber. And boring. And intellectually stale.