Originally Posted by Double X

Physical discipline teaches kids to accept rules when something is more powerful than you, to not think for themselves. It promotes the idea that violence can be used to prove you are right and you can use it to control other people. If a child sees a parent using violence for anything, they will be more apt to do it as well.

Lecturing them (which can be equally as painful) about why certain things are wrong is a much better option, as it encourages them to think logically about their actions.