One thing to remember about online communities is that size is by far the most important factor. Things work very differently at different orders of magnitude. If you know of a community of HN's size or greater (millions of users a month) where snarky dismissals have helpful systemic effects, I'd like to know what it is, because I don't currently believe that's possible.
As for flagging, what thread are you referring to?
Regarding the rest, I’m happy to simply disagree with you having observed this in practice in other communities. It’s not black and white.