The one time I remember being spanked as a child was -- many, many years after the fact -- explained to me in passing to be for the exact reason you describe. It seems neigh impossible to me to validate that the spanking was "necessary" in any reasonable interpretation of the word; sure, I was never hit by a car as a kid, but you can't really prove a negative either. I can say, unequivocally, however, that 2-year-old me experienced the spanking as a completely arbitrary and utterly humiliating display of violence with absolutely no rhyme or reason whatsoever.
