It is interesting how polarized this gets. Our vet is a big proponent of positive based training. Heck, he doesn't have exam tables in the standard rooms. He just gets right down on the floor with the dog and reserves tables for procedures where they are needed. But even he says you need both positive and negative reinforcement, especially with some dogs. The form of the negative reinforcement is key ("no", or a yip/pretend pain and stopping the fun activity or ignoring them, etc.). False dichotomies are, well, you know.