In thinking about an answer, you made me realize one of the things I love about HN: trolling or negativity for the sake of being negative isn't allowed to accumulate attention (in general). It is dealt with swiftly and the discussion moves on.

Sure, there is negativity in the form of criticism, but that's part of a healthy discussion, IMHO.

It's not perfect, but does it a lot better than other discussion forums where people discover that negativity can give them a higher profile.