Well for one, man was made superior to animals.
There is a difference between child abuse and tough love. As it was stated by Raptor, a good spanking is nothing compared to what would have happened if his parents had let him play with fire. 'Tis a substitute for non-existent instinct on the subject of fire.
Sometimes comprehension cannot be gained through speech communication, especially in early childhood. Pain on the other hand does not have to be learned, the system for it is already there.
You learn that touching something hot is bad when you get burned. It's better to have your hand slapped than lose your finger.
Now I will say that I am pretty good at english communication, but even while typing this I can't stop thinking that I could have worded it better or etc, so please alert me if you feel you don't fully understand what I'm saying.