For me, the big issue on this topic is the shelter situation. Every life is so dearly important, yet so many get killed every day as a result of human negligence and ignorance. One persons mistake isn't another person's problem, sure, but I can't help but feel that the first option should always be to rescue a dog that already exists, and needs a home to love it.
That said, the working quality or temperment of these abandoned dogs is sometimes not appropriate to what a dog owner would like to do, activity/sport-wise. This is a good reason to breed two proven animals, in the seeking of a particular trait in a dog. Or, for the guarentee of lifelong support from a quality breeder. It's my opinin that offering these things to a buyer (or to family members, if the goal is to provide animals to people you love) are good reasons to breed. Sometimes things just happen, sure, but as dog owners, who are completely responsible for the health and happyness of our animals, and as responsible adults who have a love for dogs, of whatever breed, reducing the number who suffer and get killed, scared and sad, should be a constant concern, especially when deciding whether or not to bring more into the world.
I don't really want to argue, as I know this is something everyone will have their own passionate feelings about, I just wanted to throw my opinion out there.