There's a big difference between superficial mostly-visual social status sharing and having discussions on a tightly moderated text-only forum which de-emphasizes personal identity and has no notifications.
FB tends to be a net negative while HN is the opposite (at least for me) because of the content and engagement.
I don't think there is a substantial difference. I had an account (which I've since deleted) with thousands of karma points. I was becoming obsessed with the validation of getting upvotes. And I'm somebody who never cared about likes on Facebook. But validation from the smart people here? It was addictive and really tainted how I interacted with HN. I went into an emotional tailspin if I started getting downvotes.
I think caring about that kind of validation is a separate issue from the content itself, and requires self-discipline regardless. At least discussion on interesting and educational topics is better than sharing yet another batch of vacation photos.
FB tends to be a net negative while HN is the opposite (at least for me) because of the content and engagement.