That's silly. You don't discipline a child by striking them - and that's not what "Spanking" is all about. And, "Spanking" is not about "Punishment", either....unless you are some kind of pervert.
Anyways...Spanking works very well although there is no magical formula as to how much to apply (and people seem to love those "Magical Formulas" - so easy). What spanking does it's immediatly gets a child's attention so that they stop doing something that is utterly destructive or dangerous - and can then be disciplined. In that way, spanking is like spraying a fire to get it under control. Unfortunately, a lot of people confuse spanking with discipline...and they wonder why they can't even house-train a dog, much less discipline a child.
So you're not physically striking a minor to punish or discipline them, you're physically striking a minor in order to get their attention.
Okay. Is there no other way to get a child's attention? So how we manage to get the attention of other adults and even pets without physically striking them.
This is really what gets me. You can't strike a pet. You can't strike a spouse. But somehow with children there's just no way around striking them in some cases.
And let's also be fair. This has nothing to do with adult:child interactions. It's parent:child interactions. No one here would be comfortable with another adult putting hands on your child.