I sense that perhaps Harold meant negative more than nasty. As anywhere, being overly negative gets a bit hard to take, but then being all "Pollyanna and sunshine" can also get wearisome eventually. A light touch, where appropriate, and basic respect for others will usually make even negative comments acceptable.

Then there's nasty and there's NASTY. I would venture that most of us would be OK with some reasonably well-tempered nastiness (in its various senses), but don't see any place for intense nastiness here.