The vast majority of arguments I have heard against spanking boil down to one thing: if you use force against children, they will learn to be violent.
But the last time I checked, false imprisonment and taking of property were considered violent acts just as much as battery was. So is medical treatment to which one does not personally consent. I suppose the subconscious thought is that children can hit their parents, but they can't forcibly restrain or vaccinate them. But surely if receiving violence will build a violent temperament, it does not matter whether the child has the immediate power to act in precisely the same way as the violence he observes.
Unless you are willing to forgo all forms of discipline, which are by nature coercive, as well as all medical treatment and perhaps even locks on the doors, until your child willingly consents to them, I don't see how you can raise a child without resorting to force in some degree. And if that is so, then it becomes clear that there is no particular reason to arbitrarily cut out one of many forms of force, but more difficultly a matter of figuring out which forms and degrees of force are appropriate under which circumstance for which child.
The whole violence-is-evil argument might make more sense if I really believed violence was always evil. But I don't. A soldier in a just war; a peace officer enforcing just laws; people acting in defense of self or others against unjustified violence--all of these are properly entitled to use force within certain limits. If what I want my children to learn, instead of that violence is evil, is that force is something to be very carefully used under very limited circumstances by people with the proper authority, then there is no reason why they should not see that modeled in my treatment of them.