Parents who use physical punishment are directly teaching their children that physical force is an acceptable way to get what you want. If we want less violent adults we have to bring them up believing that physical force is not acceptable. When serious cases of child abuse are investigated, they are frequently shown to have started with occasional smacks given in the name of discipline which gradually escalated into tragedies. Current acceptance of physical punishment causes a dangerous confusion. Most of those responsible for seriously injuring children are found to have been physically punished in their childhood.
Rewards work better than punishments for children, just as they do for adults.
There are already many parents who don't hit their children in any circumstances, but certainly believe in discipline and limits. You don't spoil a child by not hitting them. But there are no clear links between such social factors and the frequency or severity of hitting children. The fact is that while there continues to be confusion over what is acceptable, hitting children is likely to itself increase stress and violence within any family. Obviously other kinds of punishment can be harmful too.