Just want to add something to the debate about how your parents smacking you can affect you in adulthood. Both my dh and I were smacked as children. In my case my mum very, very occasionally (5 or 6 times?) chased me round the room with a mason pearson pure bristle hairbrush. I guess I was 4 - 8 years old. When she caught me she would smack me once on the arm. It hurt. But by the time this happenend, the adreneline from the chase, the wild look in my mother's eye, the sheer novelty of it all would make me slightly hysterical. I was never frightened. Usually ended up half laughing at her for losing her rag and often by this time she was laughing too. She would always say profuse sorrys afterwards and would let me hit her hand with the hairbrush. That was by far the cringemaking worst bit.
I have absolutely no ill thoughts about my mum slapping me. Nothing to keep me awake at night. She was a gentle, tolerant and caring mum and made me feel totally secure and loved. For this reason I personally cannot see her smacking me as an evil. I have smacked my son occasionally. He isn't traumatised, honestly take my word on this. I don't think smacking is usaully the most effective form of discipline but hey, so what? It is an absolute non issue with me personally as long as the parent/ child relationship is good and the smacking isn't brutal and routine.
But take my husband. He too was smacked by his father. I wasn't there, I can't say what happened. The beatings, though occasional have left him full of anger at his dad and they have never had an easy relationship. The last time my husband was beaten up he was 16 years old. His father (a good man I hasten to add, not a brute) refuses to remember it. My husband swears it happened. This failure to acknowledge the past eats him up still. He has gone out of his way to be a loving dad to his sons, cuddles them a lot and tries to be as different from his dad as he can be. But he has smacked our son occasionally. He says he feels guilty afterwards. That's his cross to bear.
My two sons respond differently to different forms of discipline. I see this all the time. I try to adjust my style accordingly. My 4 year old can feel totally devistated by a light slap and will run away howling. Some of that is for dramatic effect, some of it is not. I am not sure where one ends and the other begins. I do know he is someone who should never be slapped. My older son at that age would have ignored it, carried on being naughty or slapped me back.
So IME, going on the people I know best, slapping, whether you are the doer or the done to, causes very different emotions.
Slapping is wrong - much too simple a statement in my opinion.