Well, if police didn't give tickets, would people stop parking illegally? If police didn't give tickets, would people stop speeding? If police didn't give tickets, would people stop running red lights, and stop signs?
If just talking to people would make them stop doing the things they are not supposed to do, police wouldn't be writing tickets.
Do you really think that if cops did not give tickets for running red lights, you would personally start running them every chance you had? If so, that says a lot more about who you are and what garners your respect in particular (brute force and intimidation) than it does about the general necessity of tickets. Even though I have a low opinion of most people's inner morality, most people are nevertheless perfectly willing to recognize the necessity of playing nice on a personal level. Furthermore, the natural consequences of running red lights are a pretty big deterrent by themselves (because they can include a horrible, fiery death). It seems to me like we have the following kinds of people:
- People who can be reasoned with, who will not run red lights simply because they understand how doing so makes it dangerous for themselves and everyone else on the road. (People really do tend to play nice in most situations.)
- People who don't really care about that, but who realize the danger of running red lights.
- Flaming assholes who will run red lights, come hell or high water
- Flaming assholes who would run red lights but don't out of fear for teh cops' AUTHORITAAHHH
Frankly, I think people in the first two categories greatly outnumber those in the last two...and odds are, if you're enough of a flaming asshole to run red lights without sparing a thought for anyone else, you're probably a big enough jerk that you'll do it anyway, despite the risk of punishment. Except in cases where running a red light is against the law but not particularly dangerous (i.e. nobody else is around whatsoever, which mitigates the "flaming asshole" thing), I imagine the last group of people is pretty sparsely populated.
Due to the existence of people who run red lights anyway, it's obvious that punishment and threat of punishment do not work for everyone. Similarly, the existence of people who would NOT run red lights means that punishment and threat of punishment are not necessary for the cooperation of those people.
The situation is a little different for rules like speed limits though. Fear of tickets really does force people to obey speed limits (or make sure they don't exceed them TOO much) more than logical argument or persuasion. However, that's mainly because so many people legitimately disagree with the reasoned argument behind speed limits in the first place, not because they simply cannot be reasoned with as human beings. Logical arguments in favor of speed limits in general are not ironclad, and logical arguments in favor of unfairly low speed limits are about as solid as Swiss cheese. It's no wonder so few people really respect them...they're simply not that respectable.
The bottom line here is: Sometimes you must correct the behavior of someone who cannot be reasoned with, and that's where discipline is necessary. However, persuasion (with genuine moral authority backing it) works perfectly well on almost all people some of the time, and it even works very well on some people almost all of the time.
People generally learn best by having something adverse to what they want happen to them when they do something they shouldn't be doing. If you hit your finger with a hammer, would you avoid doing it again if you felt no pain and your finger was not damaged in the process? The reason you don't hit your finger with a hammer is because it hurts and you want to avoid the pain and damage to your finger. The same holds true when you touch something hot and burn yourself. The results of doing such a thing deters you from doing it again.
If people wait and let their children get away with anything they want, the children usually don't understand there is any penalty for doing something wrong. If this is allowed to go on long enough, even spanking the child will not help. A child will grow past a certain age where anything you do to deter them from doing things that are decremental to themselves or others will have little affect on them.
Discipline must be started as early as possible and continue with consistency for a length of time before a mindset will take place and the child will understand there are penalties for inappropriate behavior.
I can't really find fault with the rest of this.

Discipline is certainly necessary for raising good kids. When your kids get out of line, discipline gets them under control, and it's important to make sure they feel the just consequences of any transgressions. I don't think anyone here is suggesting that parents should let their kids run wild and turn a blind eye to their brattiness.

However, while discipline is necessary to raise truly good kids, it's still not sufficient, because discipline by itself only affects outward behavior, and it's not enough to make your kids moral on the inside (which is really the true goal). In the long run, the difference between good people and functional, well-behaved assholes is moral understanding.
Of course, when I say that discipline is necessary, I'm not referring to spankings in particular. I can see situations where they make sense, but I think there are better alternatives for most occasions.