I agree with every view on here from different perspectives, I suffered only from the indignity of a slap from my mum as a kid, as did my girls from me, yet I cannot abide the idea of my grandchildren being punished that way, but my daughters make their own minds up what constitutes punishment. What I found much worse than that was being made to feel ashamed that I had let my parents down in some way, following a verbal dressing down, which had a much longer lasting effect than a slap.
It was certainly the case that if I went home and told my mum and dad that another kid had punched me, the reply would be to punch them back harder then, likewise a kid who bit someone would usually see the error of their ways after a bite from their mum.
The world is a very dfferent place today from my childhood and parents must be the only ones to make the decisions about punishment fitting the "crime". Children who are systematically beaten as in the quoted case of Baby P among many others, are very often only "guilty" of the fact that they exist at all. Just my opinion!