Why would HN be treated differently in the long run? Facebook and Twitter are easy targets but surely the goal is to make all sizeable sites pay?
Isn't the crux of the issue that FB and Instagram (and Google) do everything they can to keep users from clicking away from their website? Thereby starving the producers of the content. HN only posts the titles of articles with outbound links, I don't think it's a comparable situation.
What do they do to keep users from clicking away? I post a link on Facebook, you click it, the website opens. What do you mean? The opengraph tags? They are opt-in, the website puts it there voluntarily. Robots reading the pages? Robots from Google, FB, etc obey robots.txt directives (and if they didn't, it's the open web after all - reproducing the title of an article is fair use).
Google doesn't actually respect robots.txt... they want you to use meta tags instead.
"I may not agree with where you post your links, but I will depend to death your right to post them" -- Voltaire, probably