The law on smacking is there to protect those who are parented by people who don't understand too far. Don't understand the fine line between loving parenting and a quite correct intent to teach a child who is struggling with right and wrong via verbal channels and subduing and damaging. Who don't understand that leaving a red mark (or worse bruising) can leave damage years after the bruise has faded.
The law is there to protect the vulnerable.
If you remove that law, you remove protection and the line which has been drawn in the blurry murky water of what is 'acceptable to society' as punishment and what is 'acceptable within a family' as punishment.
I do not believe that the State should legislate against all eventualities when it comes to parenting. I do believe in protection for those unfortunate enough to be born to the wrong people.
We should be looking to teach those struggling with errant children and violent teenagers how to deal with them better, how to be better parents, without resorting to smacking. I believe there was a time when smacking was an acceptable form of teaching right from wrong. I do not believe we exist in that time any more.
I believe we should be offering parents who are honest and brave enough some form of assistance. We should be examining why social constructs collapsed and continue to collapse.
We should tackle the root of the problem. Not 'slap' a sticking plaster over the top of the bruising and hoping it all goes away.