Hitting isn't nearly effective as using their name in a stern voice. The problem with kids isn't the kids, it's the parents. The parents don't know how to discipline them with body language and tone alone, so the kids run around doing whatever they so please.
I watch parents today compared to how I was raised, and I laugh sometimes. Moms and dads say their names like "Katie, don't do that!" But not in a stern way. They do it near or exactly the same tone as "aww, you just said something stupid, which was cute."
The children take it AS such, and don't know they're doing wrong. Children don't interpret words, they interpret tone.
Even still when my mom calls me, I can tell if she has a headache and I need to shut up and just listen to her talk. When we're trained by our parents, we won't run out of control.
Another thing is that parents can't pick their battles right; a mom I know won't let her kid do ANYTHING, most likely out of fear. The kid is about 11 months old, and she won't let him bang a spoon on a table. Why? It's noisy.
Sorry, but he's not even 1. He won't know why, nor can he ASK why. It'll just confuse him. If you use "NAUGHTY!" tone all the time, the kid won't get what is worse than the next. If you never discipline, then you're screwed as well.
Hitting is only justifiable if you've done ALL these things and the kid doesn't get it. If the violence is like, spanking, go for it. If it's touching the kid in the side of the head to get him to look at you while you talk to him, then go for it. If it's hitting the kid for no reason, THAT'S where the line is drawn. It's all about picking your battles.