It's not necessarily up to the government to say it's illegal. Particularly because a whole buncha idiots like all of you muddafockers who think kids need to get beat every once in a while would bitch about it too much.
Personally I wouldn't spank my kids. Probably has to do with experience working in childcare. I have been both a camp counselor with kids ranging from 7-17, and a daycare teacher with kids from kindergarten thru grade 5. In my experience I've hardly even needed to raise my voice to discipline a kid.
All it takes is establishing a little respect from the kid and they will *ghasp* listen to what you say.
Usual discipline process:
"What are you doing?"
"Why are you doing that?"
"Are you supposed to be doing that?"
"Okay."