Any answers to this question I would hope would cite at least one reputable source; I'm really not looking for 40 opinions. As a nonspanker, I'm frequently surprised this is still in practice around the world--probably a majority. Most of my friends (including medical professionals and teachers) start out their defense/explanation "Yeah, but ..."
My concern is: everybody has a breaking point. Traumatic stress beyond a certain level damages the psyche, permanently. That point is different for each child, and once it's reached, you're child will never be the same. You don't know when you start spanking what the cut off is for causing emotional harm rather than "education." Does the evidence suggest my concerns are warranted?
I'm not trying to come across as judgmental, and I'm not looking for anecdotes. I'm wondering if there is bona fide long-term research on this subject. I'll even accept being soft if that's what the research suggests.