Obviously this has gone far beyond the original question in some ways. It's bound to, it's a contentious issue for some and a very emotive one for others.
I don't smack, I don't allow smacking in my home. My stance is clearly of a preference for non violent means of parenting.
I don't believe for one second that smacking in public indicates further abuse in the home. IME, people who use smacking as a form of discipline aren't all that ashamed of carrying it out in public whereas OTOH, abusers are far too devious to carry abuse out in front of others.
From a sociological POV, I think violence of any kind towards children in any place is damaging to both the individual child and the community that have to bear witness. What kind of message does it give? It infers that violence is acceptable within our society.
I personally find it abhorrent. It makes me shake and feel nauseous to see a child smacked, hit, humiliated or hurt by any other means by any adult. I find it incredulous that swearing in public is illegal, but smacking isn't...
So yes, we each have a right to 'discipline' our children as we see fit, but our (society's) children have a right to be protected from those that do not know the meaning of 'within reason'- I, amongst many other people I know don't believe anyone has the right to raise a hand to a child and more to the point, that it's entirely unnecessary.
Those of us (DH and I, our children and I'm sure, many others) that do not wish to witness draconian corpral punishment, shoudn't have to.