I love how everyone uses different euphemisms for the subject of physical abuse - spanking, beating, whipping, smacking, etc. - without really agreeing on a preset definition of what we're arguing about.
For the record, I DO NOT believe that parents should administer any form of brutal beating to their children, by which I mean using their fists to assault parts of the child's body that could be easily seen by others. This does nothing but instill pure fear towards the parents instead of love or respect, and has every right to be illegal.
Now, spanking or smacking their children - by which I mean either administering a flat, possibly large item to the child's posterior at a painful, but not injury-inducing level, or using the palm or fingers of one hand to strike at a part of the child's body in a light enough manner to not cause injury, but in a heavy enough manner to illicit a response from the child respectively - I do not see as wrong, immoral, or illegal, and should be a part of raising, at the very least, a young, pre-teen child.
Children, and I do mean Children, not Teens, need to have a certain amount of structure in their lives. Many of them are prone to doing things on a whim, without really taking the time to think if what they're about to do might be bad, either for them, those around them, or quite possibly on a legal/moral standpoint. They need to know that certain actions come with consequences, and it's up to the parent to responsibly determine what those actions are. By this, I do not expect to see a parent giving their child a timely smack on the back of their child's head every time they speak out of turn, or take them out of the room to administer a spanking if they accidentally spill their drink. What I refer to are slightly larger things.
Physical discipline carries much the same weight as swear words. If you use them too much, no one believes you're using them seriously anymore, and will typically dislike/hate you the more you use them. But if you watch how you use them, wait until a specific moment that calls for nothing short of something truly unworldly, than they carry with them an unbelievable potency, and those who are audience to this act feel the weight of that moment all the more. Conversely, if they're never used, one could possibly be considered a calmer, kinder, gentler person because of it. But good guys are typically among the first to be betrayed, undermined, or outright ignored.
A child needs to respect their parents. They do not need to fear their parents, but they do need to respect them. Some people believe a child that does not receive any discipline feels himself to be invincible. This is only a half truth, IMO. I believe that all children believe themselves to be invincible, and it's up to their parents to show them where their limits lie, whatever that may entail. Physical force is quite possibly the fastest, easiest, and only through consideration of the aforementioned, the most effective means of asserting authority and administering punishment for an action. However, as many have shown, it is not the end-all-be-all answer. Once again, however, there aren't many forms of "nonviolent punishment" out there that really seem to work anymore.
I mean, think about it. Nowadays children have Cell Phones, the Internet, various types of Video Games, TV, music, and more and more are gaining access to these things in their own rooms. For "Grounding" to hold any kind of weight, you'd need to go to the trouble of removing all of these all at once. If you simply send them to their room, you're just doing what most kids would want to do anyway. If you cut the Internet and Cable from their room, they'd still have their video games. Cut the power from the room completely, they'd still have battery-operated things like DS, iPod, etc. And god forbid if your kid likes to read, but I suppose if you have a kid that likes reading maybe you're not so bad off. You'd have to go to incredible lengths to deprive your child of things just to make it "feel" like a punishment, and even more just to make sure the deprivation keeps and the child doesn't pull out some "secret" stash and undermines everything you just tried to do. All to be a "good" parent and not "beat" your child.
Now, maybe I'm being a little rash. To those who are against spanking/smacking your kids, what do YOU all do to punish your kid when they do something wrong. And a follow-up question, how well does it really work? If you're not keeping a close eye on them, how do you really know they're being "punished" and not just sent to their room to do something they probably do already.