If Hacker News is just as much 'social media' as less literary platforms like Twitter or Facebook, then I don't think that social media is the problem per se. Y-combinator has its own profit motive, but it doesn't take its readers for fools to be manipulated. (Well, maybe this happens a little bit, with people voting up trendy stories.)

Yes, Hacker News has a 'share button'. I think what sets it apart from sites like Facebook is that it's not sufficient for the shared item to garner lots of attention; rather, it will be subject to written criticism, potentially leading to downvotes and flagging.

Finally, Hacker News is moderated by very thoughtful people, ruling out a big chunk of the content that makes unmoderated social media little better than a tabloid magazine.