Are you aware of any other forums with high quality discussion? The quality of discussion here can be found occasionally in a few subreddits but they are even more niche and users have less decorum overall.
That was back in the early 2000s where if people wanted to protest against a forum's new policy, or a decline in quality, they'd just boot up a fresh instance of phpBB and essentially 'fork' the community. I don't know anyone back then who hadn't had experience setting up and modding a phpBB board, or dealing with vBulletin and Invision Power Board. I kind of miss that because now we just have various SaaS that run managed communities through apps...
There are likely plenty out there, but you're probably looking at niche forums that require some time and investment to become a part of. HN is one of those. Reddit will only offer you so much.