I think smacking/hitting/spanking is always wrong. I don't believe spanking is any better, or that infrequent hitting is better, because victims of those exhibit the same behaviors as those of frequent abuse. They believe they deserved it, that they were doing something wrong, that they were a willful or naughty child, etc. It clearly damages self respect. My partner who was abused by his parents (hit with a belt, smacked across the face, hit with whatever object was nearby, bad enough to cause serious scarring) has the same attitude towards smacking as my friend who was spanked as a child, though their experiences are far different. The real issue seems to be the fact that the child/animal/adult turns in in on themself, and thus critiques and changes their very personality. It's unbelievably damaging, even in small doses.