Okay people, listen.
Anyone who thinks spanking is an act of violence obviously shouldn't spank their kids.
Spanking is not intended to be violent - it's intended to teach a lesson not to do it again. If done properly, it leaves no marks physically, emotionally or psychologically and the pain is temporary - very temporary. The lesson learned, however, is hopefully far more reaching. Yes, you can be sued for striking an individual, but honestly, and everyone knows it, most people use that as a monetary gain. If someone slaps you, the only thing that is really hurt is your pride and you know it.
Some kids never need a spanking. Some do.
A parent and only the parent is the ONLY one in a position to determine what method is best for their child. Whichever method they choose should NOT be abusive, whether that be physically or verbally. Discipline can be administered with love, whether that be verbally or physically, and that comes from one who has received and administered loving discipline from authoratative figures.
Kids that are spanked do not necessarily grow up to be violent. I was spanked, often times i felt it was borderline abuse, but nonetheless, i'm the least-violent adult ever now.
Comparing a spanking to slapping a co-worker or spouse who doesn't listen is totally absurd - there's NO COMPARISON. It's something directly associated with the upbringing of children. They aren't old enough to determine right from wrong, and so they need an authoritative figure to teach this to them, and spanking is a way to enforce it if necessary.
So a parent should use his or her intuition and discretion in determining what form of discipline is best for their child. Anyone who thinks they have the right to state that a parent is abusing their kid if they spank them (properly <on the buttocks> and unabusively) needs to be quiet, for they are not in a position to make such a statement.