I think (and I quite acknowledge that I'm pulling this out of where the sun don't shine, I ain't a parent) that the issue with many 'discipline problem' kids who 'need' to be smacked a lot, yelled at, etc. is that many parents don't grasp or accept that day to day discipline is hard work. Teaching kids 'no means no' early on sounds like a good idea (because it is) but it's a job of some serious work, and will come with a lot of aggravation, some tantrums, some 'i hate you mommy's. But it will pay off later. I think a lot of parents look for a quick fix, something they can do that will immediately turn their kid into an angel in one easy session at no cost to them. Yelling and screaming and hitting achieve more instant results, so they do that. The fact that the results are much more temporary means they have to keep doing that.
I agree again, even though I am also pulling it from The Place Where The Sun Does Not Shine, because I am not yet a parent either

.
I
am a parent, and I agree with both of you.
You have to start early. You
have to. They have to learn early on that "no" means "no," and if you tell them to do something, by God, they'd better do it. There's no need to be an ogre about it, though. My two oldest kids are 4 and 2 and they clean up their room on their own. It's not that hard, either. "We won't go to the park until your room is clean." Or, "You can't swim in the pool until your room is clean." They go in there and tear it up, they're gonna pick it up before they go do something else.
The only time they really get spanked at all is if they do something they absolutely should know they aren't supposed to do, like go outside by themselves without asking, or feeding their food to the dogs. Those things happen rather rarely because we didn't let it get out of control in the first place.
You always start with gentle redirection and work your way up. You don't go straight for the swat.
I've met parents who just plain didn't discipline their kids at all. These are the kids who are holy terrors by age 7, and end up hopped up on various pills because they never learned how to behave and it's easier to just screw with their brain chemicals than actually discipline them.
By contrast, I am very much against medicating--I see it as a last resort when all other therapies have failed. Our daughter had seizures when she was an infant, and we gradually weaned her off of her meds when she was 2, to see if she would do okay. The doctor wanted to keep her on the pills forever. Well, she hasn't had a seizure in two years, so she's probably outgrown it. We'll see.
In short, I think a lot of parents use spanking as a "quick fix," the same way they do everything else. There are no quick fixes. It takes persistence and patience.