If true, then that is tragic, but let's not create a nanny state over the exception and not the rule. The vast majority of people who got spanked as kids were not the subject of Torquemadian torture. Spanking your kids is not usually the slippery slope down evil.
I don't want to create a nanny state either. But, anytime marks are left, a review should be conducted. This will serve as a warning to parents who are going to far or have the mind set that will cause them to escalate.
The second time this happens, the parents should be ticketed and required to attend anger management.
The third time they should be charged.