This is all good stuff.
It's impossible to be 100% positive. The idea is to practice reward based methods. In otherwords, we're dealing with adding or removing appetitive stimulus to make behavior happen or to stop behavior. By dealing with appetitive stimulus instead of aversive stimulus, we run minimal risk of hurting the animal. It's a matter of ethics. If you were able to equally effectively teach a dog to sit using either food or by pulling up on a choke collar, which would you choose to do?
The other thing is, people who use aversive punishment tend to become addicted to it. When the dog is misbehaving, we want to make it stop, so if we use a quick punisher and it stops, it's a very rewarding process for us. Because it was so easy to do and required very little forethought to pull off, we will tend to use it more in the future. As the dog becomes accustomed to pain or yelling, the less effective it becomes, and the harder your punishers have to be to stay effective.
Dogs are in fact, not pack animals. That is a myth that still lives on.