Why do intelligent people spank their children?

Why do intelligent people spank their children?
If we are intelligent people, most of us educated, if we are thinking people, creative people, then why is the spanking of our children not frowned upon? I say we, but I don't really mean me. I do frown upon it, and I don't practice it. What I mean is this: why do intelligent people spank their children? It is something I expect out of the ignorant, the uneducated, the non-thinking peoples of this world, the people who come from a long line of other ignorant, uneducated, non-thinking people. I don't expect it from the smart ones.
Firstly, it doesn't make any sense. A couple who feels it is very wrong to hit one another out of anger or frustration will hit their children out of those same emotions, or even worse, to get their attention or prove a point. If I hauled off and struck my husband, whether on his face or on his ass, just to prove a point or get his attention, I would be considered an abusive spouse, and he's a grown man who can defend himself. Why is alright, in our society to strike a helpless child? Yeah, sure, you're not punching the child in the face, you're hitting him or her with an open hand on the behind, or slapping the back of his or her hand. But isn't hitting hitting? Certainly a punch in the face is painful, but a slap on the ass is humiliating. Why would anyone want to humiliate their child? Why would any intelligent and loving parent want to hurt their child's feelings and make him or her cry? Not only is it cruel and ignorant behavior on the part of the parent, it also sends a mixed message to the child.
We tell our children not to hit others. When they play with other kids and hit out of frustration, they get in trouble. Some parents put the child in time out, which makes sense. Other parents spank their child and say, "it's wrong to hit!" I suppose these same parents also bite their children to show them that biting is wrong, and will someday light up a cigarette while telling their child not to smoke. It's the hypocrisy that kills me, well, that and the hitting itself. These parents that hit, oops, I mean spank, right, because terminology is everything? It's these parents that say, "I was spanked and I know not to hit people." But did they know that at the time? As small children, did they understand that? "It's ok for mom and dad to hit me when they're mad, but it's not ok for me to hit anyone else, including mom and dad, when I'm mad?" Yeah, that makes lots of sense to a child.
I just can't get my mind around it. It's basic common sense, not to mention basic human decency. I can't even fathom striking my child, on her butt, hand, leg, anywhere. I couldn't raise a hand to that soft, tender flesh that I held in my womb. I couldn't bring tears to her sweet, innocent eyes out of violence. I honestly don't know how parents do it. Intelligent or not, I don't understand how they are even able. Are we not beyond violence? As intelligent people, as creative people, can we not find better ways to communicate with our children? In this day and age of information, can we not read about the psychological effects of spanking on children? Or are we still of that ancient mindset that anything our parents and parent's parents and parent's parent's parents did is still ok today? Can we not move forward into a new age of communication and understanding? Are we such base and primal animals that we can't use our minds in compassionate and creative ways? This is something that I just don't understand. Spanking is hitting, hitting is wrong, hitting is abuse, hitting is something base and primitive; it is not an action of the evolved mind.
If I have offended anyone, well, so be it. At least I didn't hit you.