Why do children — and adults — behave as they do? The answer always lies in the feelings. Feelings lead to behaviors. Feelings are the motivators of our actions.
The problem with physical punishment is twofold. First, physical punishment elicits precisely the negative feelings one does not want to generate in children, namely, distress, anger, fear, shame, and disgust. Second, physical punishment squashes precisely the feelings one wants to encourage in children, specifically interest and enjoyment.