I started training about 2 years ago with just my own dogs, now I work with dogs almost daily. At first I was definitely in the "positive reinforcement only" boat but as soon as I was met with my first behavioral issues to fix I learned very quickly negative reinforcement and positive punishment is very important to success in training with behavioral issues. I don't do hitting, yelling, or anything like that. But leash pops, a little tap, etc is very useful and won't harm your dog. Dogs correct eachother all the time, it's natural. You have to learn to do it correctly of course or it can negatively affect the dog. I'm in no way a professional, but I do plan on being one someday so this is my educated opinion. I reward my dogs for doing correct, I correct them for doing wrong, and my dogs are doing pretty good, they both have ribbons in obedience and rally.
I don't understand why there is so much controversy with using treats, if they are properly phased out you're dog should listen to you without them. If you just cut them off cold turkey, that may not be the case.