He further claimed it did not matter much whether parents had a strict or relaxed attitude to child rearing. What mattered was that they loved their kids and enjoyed their company, spent time with them, and were reasonably consistent. Grand parents and other adults could augment the contribution of the parents.
The concern about parental smacking arises mainly because such “punishment” ranges from “reasonable” mild punishment to alcohol or drug-fuelled lethal (child murder) and worse. And I do mean worse. To some it seems safest to try to protect children by prohibiting any form of physical discipline.