I think there's another factor that is subtle but powerful: comments are forever. You can't edit or even delete your comments. So unless you really screwed up a

I think there's another factor that is subtle but powerful: comments are forever. You can't edit or even delete your comments. So unless you really screwed up and convince a mod to delete it for you, that comment's going to be up there attached to your handle. At least for me, that makes me much more careful about what I say. Not that I'm in the habit of deleting or second guessing posts after the fact on HN or elsewhere, but the awareness that you're chiseling in stone makes for a different mindset.