Spanking can be as mild and non-traumatic as a little swat on the clothed buttocks or as severe and traumatizing as a bloody beating. Verbal "chastising" can be as mild as a gently "That behavior is not acceptable" or as severe and damaging as "You worthless little piece of sh*t, I'm sorry you were ever born and you will never amount to anything! Now go outside and play in the traffic!"

Well, you get the point.   People can abuse a child with almost any form of "discipline," and many a child would probably prefer a slap on the butt to being deprived of affection and approval for an extended period or having horrible things said to him/her.   Moreover, any 'system' of discipline is ineffective if it's arbitrarily and inconsistently applied.

Ironically, I think if there's any age when spanking might be more useful than other forms of discipline, it's during the pre-verbal years.   No, I'm not recommending spanking babies.   It' generally "overkill,"   But in the first year or two of a kid's life, you can't ethically withhold food or use "time outs" without risking being MORE abusive than you'd be if you gave the kid a slap on the tush. "Reasoning" with a toddler isn't gonna work. And I think things like yelling "Bad boy!" may do more lasting harm than moderate spanking.

The most important point is that you're not going to turn bad parents into decent ones by legally specifying what form their (bad) parenting may take.   Yes, the law should step in when parents produce injuries or use "cruel or unusual" punishments, but a total ban on spanking before age 3 seems not only unnecessary but bound to penalize many a reasonably responsible parent.

What're you gonna do -- take a two-year-old away and put him in a "loving, caring foster home" because his mom or dad spanked him/her?   Yeah, that'll really help.