I think if you are just having a pet dog to have at home then your should get it spayed/neutered. There are way too many dogs living in shelters without loving homes, and too many dogs getting put down because no one wanted them. However, I also think it is important to keep purebreed dog breeds alive. Hence, you need breeding. And most breeders make sure that their pups are going to go homes where they will definetly be wanted. Plus, without breeding there would eventually be no more dogs left on the planet. But I cannot stress how important it is to spay/neuter your pets because shelters are too full!
My dog is from a shelter, I wish I could take them all in It's so sad to see so many loving and beautiful dogs without homes.
Of course, I think puppymills are AWFUL!!