do dogs have a need to breed? Discussions

I had an interesting conversation with my grandfather about dogs and their 'need to breed'. He once had a German Shepherd named Queenie who basically did as she pleased. If she wanted to chase a cat, she did. If she wanted to help herself to what was in the fridge, she did. If she wanted to go prowling for dogs, she did. She never had a litter though, which my grandfather attributed to her high standards of picking a mate. Had she found a dog she wanted to have puppies with, he would have let her because according to him, dogs should be allowed to breed if they want to. I remember hearing theories over and over again when I visited vet offices. People did not want to spay their pet until it had a litter, since that's whats better or what it would want or what is healthy. How could we...