The short answer is that the day I graduated from veterinary school I took an oath that said: “do no harm”. Using punishment in training or in the behavioral modification is not without potential side effects. As a veterinarian, when I am treating a bacterial infection in a patient often I am given a choice between two antibiotics. Both antibiotics are equally effective at eliminating the bacteria. Antibiotic A has no side effects but antibiotic B has potential side effects, some severe and there is no way to predict which patient will have an adverse reaction.
I will always choose antibiotic A. I am not stating punishment does not work, it absolutely does but with potential side effects. Positive reinforcement does the job with no side effects. I strive to only practice science-based medicine, there is plenty of research that supports positive reinforcement training techniques that produce better results over shock collars. Please follow the link below for more information. https://www.companionanimalpsychology.com/2018/06/study-outlines-reasons-to-ban.html
Many of the dogs I treat for behavior problems have a history of some form of aversive training, typically in the form of what is referred to as “balanced” training. Balanced training does employ some form of positive reinforcement paired with punishment in the form of choke collars, prong collars, or shock collars also known as E collars. Using aversive forms of training can be very stressful for dogs because the methods utilize either the threat or the administration of pain if a particular task is not performed. If you put two dogs side by side and ask them to perform the same task, I can always pick out the dog that was trained with positive reinforcement methods. They exhibit a more relaxed appearance, and quite frankly, they look happy. They perform the task because it was taught in a fun way. Whereas the dog trained with aversive has a more rigid body posture and exhibits more stress signals in its body language. Many times these stress signals may not be recognized by the average pet owner.
I have seen horrible human-directed bites secondary to shock collar training. I have a close friend and colleague whose grandmother nearly lost her arm because she was standing next to her dog when it was being trained to stay within the borders of an underground fence. The dog was shocked and it violently redirected to its owner. Sadly, the dog was ultimately euthanized because of this.
It can exacerbate dog-on-dog aggression. If every time a dog looks at another dog and is given a “correction” it simply reinforces the notion that other dogs are bad, ultimately making the problem worse. I often treat dogs for phobias to noises such as a microwave beeping because it has a similar sound as the warning noise of the shock collar. I have had cases where the dog was terrified of a cell phone on vibrate because it reminded it of the vibration warning of the shock collar.
The American Veterinary Society of Animal Behavior has a position statement that condemns the use of aversive training techniques such as shock collars. Many European countries (Germany, Norway, Sweden, Denmark, the United Kingdom, Austria, Switzerland, and Slovenia) and parts of Canada and Australia have banned shock collars. In the United States, Petco has permanently removed shock collars from all of its stores. I hope that other companies follow suit.
Unfortunately, there is no oversight of the dog training industry. Literally, anyone can call themselves a dog trainer. It is hard to know who to trust. Sadly, I have seen many dogs' lives ruined because they were sent to an aversive trainer. My best advice is to do your research. Ask for their credentials and research the meaning of the credentials. Ask if they are members of any professional dog training organizations. The American Association of Professional Dog Trainers, Pet Professional Guild, and the International Association of Behavior Consultants are the three that have the best reputation and prohibit the use of aversive training techniques among their members.