A Private Members' Bill is being put forward by Scottish Green MSP John Finnie that would remove the legal protection parents currently have.
Rev David Robertson, who also founded the Solas Centre for Public Christianity, says it's a ridiculous idea because it would criminalise parents and waste resources.
He tells Premier: "It's already against the law to hit a child on the head or to hit with an implement or to shake. "Take my own three kids. My youngest daughter was as stubborn as anything and so smacking wouldn't work, whereas sending her to her room was much more effective.
"Criminalising someone for smacking their child on the hand or a slap on the leg is ludicrous."
He also says any new law would be unenforceable: "I think it is absolutely..... it's insane to be honest. It's unenforceable because how would anyone know? It's just encouraging 'busybodies'."
And, he went on to dismiss any religious reasons for such a move:
"Personally, I don't think the verse in Proverbs about 'Spare the rod and spoil the child' is insisting that we have to hit our children. I think what it's saying is that we have to discipline our children."
Rev Robertson also said there are more important things politicians should be focussing on, such as poverty and inequality.
Other critics of the proposal have said any conviction for assault could harm a parent's employment prospects. They also say it's a waste of police time.
The Scottish Government has said it is against physical punishment but currently has no plans to introduce any legislation.
Click here to listen to Rev David Robertson speaking to Premier's Nick Hull:
*Correction: This article has been corrected to clarify the Rev David Robertson is a former moderator of the Free Church of Scotland.