Overall, I'm dubious about the idea that negative reinforcement (a.k.a. punishment) is fundamentally ineffective, since fines and jail sentences do seem to work as a deterrant.

I think the general notion is that negative reinforcement teaches you to avoid being caught, while positive reinforcement is more likely to make "being good" part of your self-image. The difference between wanting to be good, and wanting to appear good when others happen to be watching.