This could be a springboard for an interesting discussion on the privileged status of parents to do things to their children that would be blatantly against the law if these things were done by anyone else. Many of our attitudes on this subject have been grandfathered in from an era when children were property, and therefore don't make sense in a modern society. Public misbehavior is public misbehavior. If spanking is ever a positive disciplinary measure at all, then how does one justify that spanking may only be administered to a child by its parents or guardians, without appealing to "because that's the way it is"?
Is it that spanking only works, or is only non-harmful if the child is totally dependent on the spanker? I would demand to see scientific evidence in support of such a claim.
Is it that enabling people to discipline other people's children via spanking would cause a breakdown in law and order? I doubt it. History reminds us that, once upon a time, a person could spank someone else's child. That's all been outlawed or stigmatized. (Remember the Simpsons episode where President Bush spanked Bart?)
Yet the parental prerogative to spank remains. I'm less interested in the controversy of spanking itself than in the puzzling truth that parents are still, even in this day and age, recognized to have extraordinary, exclusive powers over their children. Essentially our society still operates as if the parent always knows best, which has been proved untrue--and is demonstrably untrue just about every time you see a messed up kid. (Indeed, by definition, if the parent knows best and has the most authority over a child, the parent bears the greatest responsibility for that child's development.)
I think the very premise of a "parent" is simplistic enough that it has become obsolete. We ought to take a look at the many influences in modern society that are shaping our children, and reevaluate the question of who should have what powers.