Earlier quoted context omitted.
Seems like restricting posts but not comments from a fresh account would thread that needle pretty well?
I'd suggest: new accounts are read-only for at least a week. Then they can comment (rate limited at first, gradually relaxed) and vote, and then after some additional amount of time and/or karma they can submit a post. Maybe some of these mechanisms are already in place? Bots can probably game this too but drive-by bots maybe won't be patient enough.
I was able to have discussions where one party has significantly unpopular opinions. Such discussions are unique to HN, please don't kill them.