Earlier quoted context omitted.
Twitter has become the de facto standard, so IMHO moderation should only ask one question: "is this tweet legal?" If the answer is 'yes' then it should be allowed. Of course, a corollary is that they should be able to filter content on a per country basis because, obviously, what's legal differs from country to country, but I think there is no escaping that for any platforms which claim to be global.
Sounds like a great way to foster a community filled with racist, unwelcoming, and generally toxic but perfectly legal content. Just like every other "free speech" platform devolves into.
It's shocking that HN commenters could be so toxic, indeed.