Also, the technical nature of HN attracts a different kind of users, who are more open to deep discussion on interesting topics. That's just a part of hacker personality I guess.
For socializing with an audience, a platform like HN is a lot better than FB. For personal communication, Email is still the very best thing we came up with, even though we can video chat, make VoIP calls or instant message. To me, Emails are an entirely different form of communicating, just as letters were back in the old days. Almost every other form of telecommunication tries to mimic real life conversations in one way or another, Email doesn't. I like that.
Bottom line: There's nothing except for advertising and handling sensitive information carelessly that Facebook is truly good at these days. But that's - as always - probably just an opinion.
Too often, then, people get into arguments that are really nothing more than "cultural crosstalk" (affecting everything from word/idiom choice to argument style); it also makes it more difficult to interpret things people say, as we normally smooth over common mistakes by way of the implied context of knowing who the other person is, and thereby can predict "what they meant".
(By the way, totally unrelated, but I can't reply there anymore, and no one else did at the time: yes, AFAIK had you implemented Amazon's one-click system, even without knowing it existed, you would have been liable; however, you would only have been subject to "damages" and not to "treble (triple) damages", which is designed to punish people who knowingly disrespect patents.)