It's an interesting question: How do you define the line between a 'forum' (which most don't consider addictive or harmful), and 'social media' (where there is growing evidence of addiction and harm)? What are some attributes of social media that are missing on forums?

Opaque ranking algorithms?

Human curation / moderation?

Automated curation / moderation?

Voting / flagging?

Infinite scroll?

Images and/or auto-playing video?

Advertising inline with posts?

Profit motive to get users to do certain things?

I don't know where you draw the line, and what makes Facebook harmful but Hacker News not harmful.

Dang has spoken about this at some length in interviews, but the critical element is whether or not we're all seeing the same thing or not. HN is special in the world of social media because the front page is the same for everyone. That makes it quite a bit different than other social media sitesfolks mention (Twitter, Bluesky, Facebook, Insta). It means the algorithm can be tweaked for engagement (like demoting stories that have more comments than upvotes), but that you can't optimize per-visitor, but instead across the whole population. That one simple feature makes a world of difference, in my opinion.