I surely do agree there are many parents who hit/beat/spank either in ignorance of how to actually train/teach/nurture or else just out of convenience or whatever, but that does not prove anything other than their ignorance or sloth.
Let me give you another scenario ...
I have a granddaughter who is developmentally challenged, and she simply would *not* voluntarily eat *anything* other than cookies or ice cream and such. As part of some on-going therapy, my son-in-law was shown how to place a little food in her mouth and then stick one of his fingers in her mouth and stimulate her tongue and cheeks so she would hopefully develop the instinct of chewing and swallowing, but she still just would *not* eat anything other than sweets on her own.
Spanking was then tried a little bit and did seem to get her attention, but I could easily see how that would eventually do harm ... and so, I began using a spray bottle (like for Windex or whatever) with clean, cool water. She truly hated that water hitting her face, but then I would quickly and gently wipe her face and give her a simple command: "Eat." I suppose we could have had a tube placed into her stomach or something, but that little girl ultimately had to learn to obediently eat even thought she had no idea what it would have meant to die if she did not.