You are drawing conclusions where there are none. If your logic were true, all kids that got spanked would turn out well.I can vaguely remember having my breeches pullled down in the middle of Walmart by my mom when I was five or six years old because I was having a hissy fit. You know something? I never did that again. Kids today are spoiled rotten because people say it's "wrong" to spank, discipline, punish, or even yell at your kids, and the result is a bunch of kids and adults who think they can do no wrong and that nothing can touch them. There is nothing wrong with spanking at all. Kids need discipline sometimes, and occasionally they need to be taught a lesson. A spanking now can prevent a loss of character later in life.
The conclusion that I'd draw is that parents that spank tend to care enough to do something about bad behavior, or are intelligent enough to know a behavior needs to be stopped. It's just not a very effective way because it shows violence is okay to your child.
I'd be more concerned about parents that have kids that constantly misbehave and they are too dumb to do anything about it.