Don't know if it's JUST southern/evangelical.
I personally don't know where to draw the line, as I was spanked myself as a child (my parents were Catholic immigrants). Belt, no buckle, two hits on my behind as I lay face down on my bed, no cussing or anything on their part, and I had to stay in my room for about an hour after it happened. It stopped around age 7 or 8, though. I don't think it did me irreparable damage although I sure cried during the time. I've probably been spanked about 10 or 12 times total, though, and they were for usually hitting my own sister.
It would be hard to watch happen to another child, though. I get really upset when parents slap their children in the face in public and was almost close to throwing a punch of my own at one point.
But I don't agree with passionate beatings as if they themselves are THE answer. Sometimes it's a time-out. Sometimes it's a spanking. But I think that at the very least, the latter should be a last-resort option. And I don't condone outright beating in anger. The stories described are really, really sad and disgusting.
It's like you are either spoiling the child or beating him. Do these people not know of a middle-of-the-road option?
ETA: P.S. I was raised in a northern blue state if that matters.
And other children I knew were hit, usually with belts, but this type of discipline stopped at a very young age. A 12 year old being hit raised eyebrows.