Melissa, Anko was a GSD from east german working lines, pretty hard by the standards of a lot of dogs out there.
In the beginning of her training, yes she would have completely gutted and eaten our cat, chickens, or rabbit IF given the opportunity. She would have also killed another dog or gotten both of them seriously injured in a fight. However, we never gave her those opportunities. We also made sure to carefully avoid triggering those drives while conditioning them out of her.
Did we say, "Anko, please stop barking and aggressively lunging at that dog," on walks when there was another dog? No, that would be stupid. We would turn around and leave with her to avoid the trigger until she learned that other dogs were OK. It took a few months of conditioning to get her to ignore those things, but it did work, and was very reliable because we made it worth her while. If we had an e-collar on her and zapped her every time she barked at another dog, there is no way on earth she could have progressed to actually playing with other dogs and having fun. A dog that is corrected physically I could never trust unsupervised. They are only behaving because they are scared you will punish them for doing the "bad thing". If you are not present to punish them, then what guarantee is there that they will not do it? If a behavior becomes a rewarding thing for them to do (like not eat the cat vs. eating the cat) then they will make the "right" choice, regardless of whether you are there to enforce it.
If you want to use the antiquated argument of humans being the "alpha" wolf in a dog pack, look at it this way:
In a wolf pack, if the alpha is not present for whatever reason (out hunting, cruisng around, at the office, whatever) then the role of leader at that present time is temporarily deferred to the "next in line". If your dog is left alone, then your dog become his own leader for the time being.
Now think, what decisions are a dog that has been punished for "bad behavior" going to make when no one is there to guide him? If he was hit for barking and lunging at the fence when people pass by, will he still not do it when you are gone? He may or may not. Compare that to a dog who has been conditioned to believe that people walking by his fence are a positive experience. He will not lunge and bark at all. Anko was conditioned to believe that our cat sleeping with her on her bed was the best thing that could happen to her, so that even when we were not around to supervise them together she would still respect the cat and enjoy sharing her bed. If we had hit her every time she looked at the cat, she may or may not have kept ignoring her. We might have come home to a bloody mess.
Frankly, no dog should be put in a situation where it could chase a car or livestock unless it's been conditioned out of it. I really don't think most should be put in that situation at all, just to take all risk away. Some dogs also just have very strong drives one way or another (like some dog aggressive dogs) and can only be taught to tolerate those things when their owner is present. That is fine too, but hitting a dog to suppress a drive is completely wrong IMO and makes for unreliable performance.