There is no way that I'm publicly going to say that it's OK to hit your kids! And you are not going to find any publication advising or even defending it. But there is a such thing as a "Physical Correction."
However there are strict guidelines to physical correction.
Must be measured, and NEVER out of anger or frustration.
Must be last resort.
Must NEVER be abusive.
No opportunity for logical reasoning.
Must be to prevent imminent physical harm.
I must say that I've been working with kids, both personally and professionally for three decades, and I have not once ever in all of that time needed to use a physical correction. But if a two-year-old is about to stick a knife in an electrical outlet and you give him a slap on the hand, I don't see CPS knocking at your door. In such a situation there is not time to explain it rationally, and the toddler would not understand the gravity even if there was. The slap on the hand, along with strong verbal commands, creates a negative association with the behavior. Theoretically, the next time the kid wanted to do it, he would think back and say - "Hey I'll get hit if I do this." But even that type of thinking may be too much to expect from a two-year-old.
Summary
There is a difference between a spanking, a physical correction, and child abuse. A spanking is a punishment after the behavior, a physical correction is measured response before the behavior, and abuse is malicious. Again, I can't publicly support even spanking....But I was spanked, and many other people were spanked, and it didn't traumatize us. The kids who were traumatized experienced abuse. Even so, the goal is to communicate with your child so effectively that spankings or physical corrections are never needed.