Online spaces cost a lot of money and manpower to run. Half the people on this site could put one up in a day, but who would pay to scale it if it wasn't monetized? And as soon as it is, you have an opaque corporate hierarchy directly MITMiddling discourse.
Wikipedia and Archive.org provide clues to other ways this could be addressed, through nonprofit donations, but then you have a somewhat opaque and unelected priesthood moderating things.
HN gets around it by basically being niche enough to rely on one overworked person to moderate. Scaling up the HN model would mean many individual small sites acting independently as a patchwork of public commons.
And all the other workarounds to this problem - and I agree it's a huge social problem and a drain on society - turn out to involve some technical hack to tie patchworks together, like Mastodon.
One thing that hasn't really been tried (by a democracy), at least that I know of, is a social network for citizens run by elected committees. And this may be the worst idea of all, since it would become a natural competitor for power with all other branches of government, and would run the risk of directly corrupting national politics in any number of ways...
Basically all this is to say that running any kind of mediation at scale between random members of society is dangerous, and not just because of the profit motive, but more basically because power corrupts.