I doubt it's an either-or situation.
However, I'll note that all shelter neuter and spay, so if it irresponsible pet owners who are responsible, than it is limited to those owners who did not get their dogs from a shelter.
However, I'll note that all shelter neuter and spay, so if it irresponsible pet owners who are responsible, than it is limited to those owners who did not get their dogs from a shelter.
The problem is irresponsible pet owners who fail to neuter and spay their pets.
Santa Cruz County, California, where I used to live, enacted in 1995 a law requiring neutering and spaying of pets. (A breeder's licensed can be purchased for something like $100 annually, IIRC.) The numbers of animals in the shelters dropped dramatically.
Efforts to pass a similar bill at the state level failed, however.