Ignoring the mountain of evidence that you can find with a quick search that corporal punishment in general, and "spanking" in specific doesn't work in the way people think/want it to, there's a giant flaw in logic here.

If a stranger does a thing to your kid, and you would want them arrested, why would you do the same thing?

Seriously. That's the glaring flaw in the arguments. If I discipline your kid with a single swat to the rear, I have committed a crime. One which most parents would not only insist come with legal consequences, but a significant amount would feel totally justified in using force to protect their child ( and they'd be right in that use of force, imo).

But then you want to do the exact same thing or worse and don't expect it to affect the child at least as severely as the trauma from battery by strangers. If someone is going to argue that they need to hit their kid to maintain discipline, then claiming that it only works when a parent does it is just stupid.

Worse, claiming that the affects of the trauma of an assault is magically not going to happen because it's a parent is outright insane.

That's why, even for the very limited benefits that can come from using spanking as a tool (that are achieved better by other methods) you end up with more drawbacks than it's worth.

As I said to my parents and my family regarding my kid: if you attempt to use spanking or other violence to "discipline" or "teach" my kid, that means such methods are effective. If that's the case, then me beating the fuck out of you and never letting you near my kid again is most definitely going to be effective in teaching you to never hit my fucking kid.