The vast majority of kids who receive corporal punishment/spanking/whatever you want to call it...get it far too much. Certainly disproportionate to what was called for based on their actions. And it negatively impacts them (literally and figuratively).
That's hard to quantify.
How do you define "too much" in this case?
You're right. It is difficult to quantify.
But here's the thing. Once you've started using pain as a means of discipline, you've sort of hit a wall. Because where do you go from there?
Some parents -- many, even? It's hard to say -- are perfectly capable of delivering one or two spankings in a child's entire life for serious transgressions, and the point gets across. If the parent then sparingly threatens a spanking for specific egregious actions, and it prevents those actions, then while some may feel it's not appropriate, I don't think it's anyone else's place to judge.
But that doesn't go for everyone. For some people, it worked once, and they're going to make it work every time after that. Is it their own anger issues or violent outbursts they can't control? Are they just that bad at being parents (or decent human beings?)
What I do know is that when you're striking a child in the face for minor annoyances, you're a bad person. And maybe you're honestly not aware that happens a lot in this country.
But it does.
So
that is what I mean when I say that far too often, kids who don't really deserve or require it get the rod far too often, and it certainly pales in comparison to the extreme few who need said rod and got spoiled instead.