Slashdot also had a rather sophisticated moderation and scoring system, that allowed spam (hot grits etc) to be downranked and appear auto-collapsed, whilst longer form content was upvoted and expanded by default - even if it was a reply to negative ranked content.
You may feel a personal preference for HN, or not, but they were essentially the same from the perspective of any lawyer.
In other words HN could easily keep its distinctive feel without ever banning or erasing anything, just by implementing sufficient controls that let users see what they want to see: in fact it already does via options like showdead.
If I have upvotes and downvotes, weighted the way I like, and I limit who can get an account in the first place, I can probably achieve the speech outcome I want relatively easily "without" human intervention.
Note that under this setup, a forum like HN would be basically impossible to maintain. How would you set up a publishing content that included user content without having a human pre-vet all of that content? And HN has, like, 3 moderators?
The practical end result of this would be that the Internet would split into a bunch of 8chans, and a bunch of TV stations, with nothing in-between. If you care about free expression, making businesses scared of user content is counterproductive.