Hitting a child hard enough to do real damage, or frequently, or without a good reason, is abuse. Abuse is wrong and should not be tolerated. (Our society gives way too much weight to so-called parental rights (in these cases, the kids have rights, the parents have responsibilities) in abuse cases, allowing parents who have demonstrated they shouldn't be allowed near their children ever again to keep or regain custody, but that's a different topic.) However, a rare spanking for a good reason is not abuse; it's an important tool, and the fact that we've completely deprived our teachers of its use and have almost taken it away from conscientious parents is a serious mistake.
The real value of a spanking is not in the actual delivery, it's in the threat. I was pretty well behaved as a child, not because I got spanked frequently, but because I got spanked just often enough that I knew I could be spanked if I got too far out of line and I knew I didn't like it. I got sent to the principal's office exactly one time when I was in grade school. I have no memory at all what I did -- my memories of my childhood are pretty dim and fragmented -- but I clearly remember being told to sit on the bench and wait for probably 20 minutes, with nothing to do except look at the paddle hanging on the wall. When I look back on the experience now, I realize that I don't know if that paddle was ever actually used. It wasn't used on me that day. But I sure thought it was going to be, and the thought of it got me straightened out pretty fast. I don't remember what actually happened when I did see the principal, but I know I was so relieved that I didn't get paddled that I was ready to promise to stop causing trouble and actually mean it. When I look back on this experience, I realize that the experience of sitting there on the bench anticipating the paddle was much more effective at changing my bad behavior than either any amount of touchy-feely talking or actually receiving a paddling would have been. But if I'd been a generation younger, there wouldn't have been a paddle in the principal's office at all, and I would not have believed that I was about to get spanked, so I could not have gotten that lesson. If all I'd gotten was a talking-to, I probably would have been back the next week, and once I started down that road, who knows where I might have ended up? The paddle on the office wall was what it took to scare me straight, and I'm glad today I got the lesson.
So, the bottom line is that kids have to learn that there are limits to their behavior and there are times when they have to stop what they're doing and listen to what their parents or stand-ins for their parents are saying. When they learn that without any sort of physical punishment, that's wonderful, but they've got to learn it, and the threat of physical punishment, made real by actually administering it when the threat isn't enough, can be effective when gentler methods aren't. Does that mean that it's always OK to spank kids, or that we shouldn't worry about it? Certainly not. It's very easy to cross the line from sensible use of spanking to abuse, and that's why it's tempting to just say never do it no matter what, but like most (dare I say all?) other simplistic solutions to complex problems, that's not nearly as good as understanding how and when spanking can be the right thing to do.
I've never had kids of my own and I don't plan to, and some people who have may think that's a good thing in the light of what I've said here, but that's what I believe and I thought I'd say so.