Well obviously you shouldn't inflict too much damage, but really, what can you do?
My situation I presented earlier was like this, I tutored primary schools kids awhile ago when I had free time on my hands. This one kid would not listen to a thing I was saying, wouldn't sit down, wouldn't pay attention, was disturbing other students. Everytime I would tell him off - nicely - I might add, he would cut me off and not listen to me. He clearly wasn't scared of authority and it's highly probable that his parents never hit him, especially when I saw how they spoiled him, etc.
How do you expect to deal with kids like that then?
I'm not a violent person but even I wanted to punch him in the face. Thankfully class was over so I didn't lose it.
Sometimes, rational discussions don't tend to work with children who are of an age where they should understand their place in life. A baby is beyond this of course, and obviously you shouldn't hit babies, but the instance I've brought up shows a case where physical punishment is the last resort - and no, I wasn't going to hit him, but I definitely think the parents should - whether they do or no is beyond the point, but I would be agreeable with physical punishment in this case.