I'm not sure HN would benefit from requiring a paid subscription. I think that aversion to the aforementioned criticism would be avoided even more, or otherwise replaced with sheer entitlement.
While some of these thoughts are definitely unwelcome, as they should be (we do need boundaries), I'm quite happy to engage with the mixed and low quality non-tech content either to educate myself to other points of view, or to attempt to counter them in the case of misunderstanding. And that's what a good debate is all about.
For me, that's a great experience because I enjoy being given the opportunity to be sensibly proven wrong.
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.