Without getting into the morality of physically punishing your animal, I think that in the case of Basenjis (at least) it just is not very effective. I think that negative reinforcement training is generally the "easy" way out for a lot of pet owers. It just so happens that we discovered quickly that it just doesn't work with Basenjis. It takes patience and creativity to solve problems using positive reinforcement. I also agree that an obvious disadvantage of punishing your dog is that the law of unintended consequences is such that you can train your dog to be fearful of you, which is trouble waiting to happen.
As far as the morality, I think we need to be cautious and not judge. And keep in mind that in canine behavoir, pack leaders will often make their desires known by using physical force-not to hurt, but to make a point. A smack with a rolled up newspaper may be the equivalent of nip on the rump by another dog, but I still think there are better ways. Of course, if you are hurting your dog, that is just cruel.