So you've volunteered at shelters and you've seen first hand, the animals in need of homes. You've probably seen animals turned away or euthanized for lack of space. After seeing that, the homeless animals caused by overpopulation, how can you possibly be in favor of breeding that creates even MORE animals rather than providing homes for those in need of them?
For one, I need my dogs to be 'predictable'. Working as a dog trainer I use my dogs for demos, I use them to evaluate behavior in other dogs, I even use them to evalute people. I am highly selective of the breeders I purchase from. I have to know that these puppies are socialized in such a way that I could essentially take any puppy from the litter and have a predictable training course. I train my dogs to the equivalent level of most service dogs. Because they are in the public eye, and because I take them into schools around young children, I can't take the risk of not knowing. I can't worry that a child might walk up carrying, oh let's say for this sake, a ruler, and suddenly the dog has a flashback of being chased once with one and he bolts and knocks someone over. That would be a mild reaction yet still highly undesirable. You have no idea the things people will perceive as aggression if they are unfamiliar with dog behavior.
Secondly, I work with problem dogs. I see the issues. Why should I have to live with that? I've often been told that because I'm an "animal professional" and because I have the ability and knowledge to work with problem behaviors, that I should automatically seek out those dogs and take them to live with me. Don't get me wrong, I love what I do, I'm fascinated by behavior, but I don't want to live with it nor should I have to.
The shelters I've worked/volunteered at did not euthanize for space or time constraints. I understand that happens, and while it is sad that not all of those dogs will get homes, I don't feel I should be obligated to provide a home for them when I did not directly cause the problem. My breeder has maybe 2 litters a year, sometimes, one, sometimes none, never more and never with the same dog in back-to-back cycles. She has a waiting list. Before she plans a breeding, she goes above and beyond on health checks on her dogs and then finding the best possible mate. She will not breed if there are not more prospective families than puppies. This way of breeding (which should be followed by every breeder but there are unfortunately a lot of unethical people in this world ) does NOT promote or contribute to overpouplation. Everyone continues to lump "breeding" as a one size fits all category and it isn't.
While spaying and neutering is the appropriate, responsible and ethical decision, you realize it isn't natural. Nature intended for dogs to breed. So wether they do so because an intact male wanders into the yard of a female in heat or because a breeder presents the opportunity to do so by selecting a mate and providing the opportunity, it's going to happen. You could let nature run it's course and by the power of natural selection unwanted genes would eventually be eliminated (provided those dogs were left to die and no one intervened and allowed these traits to remain in the gene pool) OR you can intervene by responsibly chosing not to breed dogs with known issues, or a familial history of issues and pair not just healthy dogs, but choose to breed based on genetic diverstiy, i.e no line breeding or inbreeding. Humans breed for "love" regardless of health. And look at what we have created! We are overflowing with horrendous diseases and genetic defects. Cancer, heart defects, blindness, dwarfism, albinoism...there are more genetic diseases, defects, and deformities than we even know about. Yet no one goes around saying "hey, you're pretty ugly, I don't think you should pass that on by having babies" or "you know, we'd like to eliminate breast cancer so because youre grandmother had it and you are at a higher risk, we're banning you from procreating". No, that's been done in the past and didn't go over so well...Hitler ring a bell? We also don't tell people to adopt kids. There are thousands of dying, starving, suffering children in the world. But no one is stopping new ones from being 'bred'. How is that any different? I have a child. Is it selfish of me to contribute to the overpopulation of the world because I didn't adopt one that was already in need? Call it what you will, I call it love and a little bit of self preservation - we all have an innate desire to pass along our genetics as do dogs.