A little slap on the ass for doing something bad is fine, as long as it doesn't bruise the child in any way, but when you go out of your way to smack your child across the face or to the point where it leaves marks, then you're just asking for your child to grow up with a low self-esteem, a higher chance of becoming addicted to drugs, alcohol, or cigarettes, or some other negative crap like that.

Hitting anybody as a punishment is abuse, although I do it to hookers all the time, but then I get in trouble with the pimp, but that's a topic for another time. And kids are still developing, so if you hit a kid, he going to remember. Maybe not consciously, but that memory of being hit gets stored anyway, unconsciously, and effects how that child grows, that child's reflexes, ways of thinking, and ultimately who the child will become in adulthood. Hit a kid to discipline, and he'll be ****ed up. Teach a kid discipline through ways in no was associated with violence, and he'll be much more likely to not be ****ed up later in life.