judge warns parents not to smack children, page-10

Kgtom, I agree.
I believe the types of parents that Free Will talks about whacking their kids in supermarkets in anger, probably were not brought up in a disciplined household themselves. I don't mean just physical discipline, but the self discipline that comes from having to keep your room tidy etc...
It DOES require an enormous amount of self discipline not to let naughty toddlers etc get to you.
Better to teach children self discipline when they are young so that they can be a good adult and parent themselves.