I've been in this field for 16 years now, and over the years that question has had different answers, In the beginning, it was just about teaching basic obedience. Then it became teaching people how to have fun with their dogs while still learning obedience. Later it morphed into teaching people with disabilities to be a team with their dog so that the dog could help them recover some of their lost independence.
Now however my views on dog training have taken a slightly different stance. I still want people to have fun with their dogs, I still coach people doing owner-training for service dogs, however now I look at it from both ends of the leash. I try my best to explain to all of my clients the dog's perspective of what is happening around them.
I belive that to understand dogs you still need a basic understanding of psychology. Without it you will not be able to see how your training is influencing your dog. We know that all behavior is driven by reinforcement, no matter if it is human, canine or some other animal.
I love working with teachers and therapists because they understand Operant Conditioning. Most of the work we do with our dogs is based in Operant Conditioning. This is the idea that learning is associated with the consequences that follow the behavior. Isn't this what we teach our children? That their actions have consequences. Why is it such a stretch to believe that dogs learn from the consequences of their behaviors as well?
For years I've been called a "cookie pusher" or been told I'm not a real dog trainer because I prefer to work with positive reinforcement rather than punishments. In the beginning, it bothered me a lot, but now I fall back on science to support my decision.
Edward Thorndike a prominent influence in the field of psychology developed the Law of Effect and was heralded as the father of Educational Psychology. His experiments lead to the idea that punishments do not work with training or education. Punishments did not weaken the bond between a stimulus and a response, however, they did increase the variability of behavior. So if a dog is punished for using the bathroom in the middle of the floor where you find it, they will start to hide where they go to the bathroom so you can't find it as easily, but the punishment did not teach the dog to go outside to go potty.
Terry Ryan a trainer who has been training dogs since the early 70's says that Training is a science, an art, and a mechanical skill and I agree with her 100%. Dr Ian Dunbar a veterinarian, animal behaviorist, and the founder of the Association of Professional Dog Trainers says:
A thorough understanding of canine behavior. A thorough understanding of learning theory. Impeccable timing. And if you have those three things, you don't need a shock collar.
Or any other use of punishments in my opinion!