I think that stopping puppy mills reduces the amount of dogs and cats being killed because they have no home. If you are a responsible breeder, and you have homes for all of the puppies, then that should be ok. But puppy mills, for one, treat their puppies like dirt, and they don't care at all for them. If more people in the world would just spay or neuter their dogs, and puppy mills are stopped, then I think that reduces the amount of dogs being killed, and more dogs are happily owned.