I think the issue is more nuanced than you think. I understand where you are coming from.

BUT

By your own logic, hackernews should be treated as a publisher, and not a platform.

Hackenews is a forum where the moderators restrict discussion to specific topics to keep discussion high quality. But I consider them a platform and not a publisher.

Or for example a car discussion forum, bans anyone who wants to discuss airplanes. Again, I would still consider them a platform and not a publisher.