Its neither, feedback supplied to the "Show HN" type posts would generally be positive, or at least constructive and polite. Even if there was no feedback to offer, people would still leave a congratulatory comment about launching.
4-5 years ago it felt like the only people who understood what you went through to launch were people on this site, everyone else including family and fellow co-workers at big corp were negative about the idea of leaving a "safe job" to pursue a dream.
But now with everyone having an idea about the next big app, and blockbuster movies coming out about the geeky kid who did follow his dream, everyone else is starting to "get" us, they can relate. So the feedback you get from outside of HN has become positive, and so the feedback from HN has become more of a "reality check".
I don't see why it just can't be polite but constructive though.
