It seems like the second someone posts a thread (on a chat forum or other online posting site) where it seems acceptable to be snarky (and dare I say, bitchy) several people come out of the woodwork who couldn't be bothered to post anything encouraging or intelligent anywhere else. This phenomenon is found in every online community on the planet. I think it is because everyone has a bit of pent up rage and saying things you would never say to someones face is way easier behind a screen.
Also, bitch begets bitch. A snark thread is the most likely candidate for snark replies.
That being said, bitch comes in all sizes and colors. I think the bitch factor goes up with the overwhelming sense of entitlement some people seem to have.
No matter where the bitch flag came from, name calling doesn't do anything to help the situation nor does it work towards improving your life or the lives of others.
Bitching and complaining is easy. Kindness and encouragement should be just as easy but unfortunately kindness and encouragement aren't nearly as entertaining. No one started chanting "hug hug hug" in the school yard, at least not that I've seen. There aren't any complement or cuddling competitions either. For the longest time (maybe since the beginning of human consciousness), conflict has been a source of entertainment. Can humanity as a species work past that? I hope so.