As for the spanking itself, it's just like a more intense version of having your ear flicked, and perhaps there exists children who simply will not co-operate with any verbal or other approach, and (in my opinion) it would be bad to constantly be at the mercy of your child's antics, desperately spending all available time to "appease" s/he to behave, all the while the child knows and developes an attitude that it can "control" it's parents to fit around it's own wants. I think a spank would stop it immediately, and would help re-establish the authority for the parent. Of course this is only in the case of really disobedient children.
You are not reading my posts. I'm not talking about asking children to co-operate or being at their mercy or needing to appease them. I'm talking about completely controlling their entire lives, and being in charge at all times. As I said, the child cannot so much as eat without your permission. You already hold all the marbles. There is no need to hit them. Unless you let them eat, play, watch TV, have company, go outside or use the computer (or cell-phone or I-pod, with an older kid) they don't get to. You're already in charge, if you know what you're doing, and you can use that to control their behavior.
"O.K., well as soon as these toys are all picked up I'll be serving a delicious lunch."
"I see you don't know how to use your manners. Do you need a lesson? Or should I just move this food over here until you remember how we eat?"
"Yes, I have a scrumptious dessert, actually, for anyone who eats their lunch."
etc., etc., all day long. You are in complete charge.
And don't forget, "What nice manners! Would you like another serving?"
Finally, it's been used in the past when we've birthed upstanding generations of people who're successfull and happy, especially in comparison to our modern equivilents, so hey - I guess it didn't do them any harm.
Your method is fundamentally flawed. Try to conceive how you could figure out whether it did any harm or not.