People have never been allowed to go around assaulting other people's children. There was physical discipline in schools but that's not comparable to this case.
I can think of plenty of adults worthy of the same treatment but that's not how a civilised society behaves.
"Civilized" society, as you call it, is what has gotten us into the mess we're in now globally. Everybody is afraid of offending everybody else, so nothing gets done so we can all be politically correct. Sometimes a brat needs an ass whoopin', and if the parents won't do it then somebody else needs to. Scolding doesn't work, it doesn't instill any respect, because after they turn about 3 they realize you're not actually doing to "do" anything. Take their toy? They have more. Put them in the corner? Can't leave them there all day. Turn off the internet? They've got toys. Ground them? Whatever. But a spanking? Fear of physical pain is a powerful motivator. I'm not saying that "every" child needs to be spanked for every misbehavior, and I'm not saying we should beat them over the head with clubs, but I totally support spanking with a belt or a paddle if it's relevant or if the child hasn't responded to more "civilized" means of corrective action, and if the kid was running around throwing things at the store clerk, and the mother didn't even witness the spanking, then obviously the parent wasn't doing her job and the kid needed to be taught to respect somebody. Now he's going to grow up with a chip on his shoulder, thinking he's "all that and a bag of chips", or whatever kids say these days, because the one person who actually spanked him got arrested.