Why I say that, well think about the physiology of your neck! It is for the most part the same as that of a dogs neck. The Vertebrae, Oesophagus, Trachea, Thyroid Gland, External Jugular Vein are all in very similar places to that of humans.
Collars are easy throw a rope or expensive piece of leather or webbing around a dogs neck and drag them along. Dogs/puppies quickly learn the game and then drag us around.
So let me go through the list of injuries that are caused by collars, Neck Injuries, Ear and Eye Issues, Hypothyroidism, Malfunction of the Nervous System (Excessive Paw Licking), Behavioral Problems. I won't restate the many articles and studies done by vets such as Dr. Peter Dobias, Dr. Karen Becker and many others.
My experience comes from growing up riding and driving horses. I think it only took me one time to learn that if I wanted my horse to move over and I pushed on his shoulder or ribs he would just lean back towards me and step on my foot. Then I was stuck with 1,200 lbs on my foot rocking his hoof back and forth trying to figure out what was under it. If I wanted my horse to work with me I'd reach back behind the ribcage and tap him near the belly and he'd move right over. While horses wear a bit, most of the control and riding is actually done with your legs and heels. The bit is just a nice contact to talk to the horse with a series of bumps but you are using your fingers not a tight fisted hand.
I wanted to create a similar feel with dogs, where I can use a nice light hand and talk to my dogs through the leash. Rather than a fist hanging on to the dog for dear life. Why the weird fit on the harness with the girth behind the ribcage? Well I want my dog to be able to move freely with minimal restriction. The control of the harness sits well back from the neck and shoulders (except for little dogs, I'll explain later). So I'm working on the dogs girth, outside his core strength. Why? Opposition Reflex, most people, dogs, animals have a lot of it. If you push their shoulders they push back, but apply gentle pressure in the waist and they will move away from the pressure. Try it on a couple of your friends and see what happens. Watch their eyes closely, when you push their shoulders their eyes tighten. Grab them around the waist and give them a couple encouraging nudges and their eyes soften and they will walk right along with you. I do that all the time as a demonstration. We want to work with our dogs like they are our best friends and have them work willingly with us.
Why do dogs pull, well dogs are predators and foragers. Watch your dog in the backyard or in the house their nose is down to the ground and any tasty morsel is gone before you can blink. There is nuisance pulling which is the dog is pulling because you have something on it that creates opposition reflex. Then there is Squirrel pulling, their chase or excitement mode is engaged. If you can stop the nuisance pulling with a gentle reminder you can then over time address the Squirrel pulling. We don't walk in a perfect environment.
Do what the dog trainers do, we've all seen them perfectly trained dogs and what does that mean. Dog trainers spend a great deal of time teaching a dog to control their impulses. That takes time. A dog needs clear instruction. Yes and a reward are a clear indicator you are happy with their performance. No and no reward are a clear indicator you are not happy. I think of a correction not as a bad word and definitely not in conjunction with jerking or pulling the dog around. But I want to send a message to my dog that behavior is not what I want. I think of it more as a bump on the harness that says we are going left not right, or a bump to remind him to stay with me and not pull me to what ever excitement maybe on the other side of the fence or on top of it.
Yes all my dogs wear collars, I think of them as jewelry, comfortable leather blingy collars with nice ID tags should anything ever happen. Yes, they are microchipped, but I don't drive around with a chip reader and most people don't. I want my dog back as quickly as possible should we ever be separated.