Neither California's SB 250 nor any other mandatory spay-neuter or anti-breeding bill we've seen yet will greatly reduce the number of dogs. Primary enforcement mandatory spay-neuter will greatly reduce the number of purebreds because it will drive away the best intentional breeders, among them most of the breeders of purebreds who sell to the general public. But the resulting reduction in the pet dog supply will be made up by 'moonshine' breeding and importing from other states.
California's bills isn't even primary enforcement mandatory spay-neuter: You'll only be forced to spay or neuter if you are caught violating some other law. As a practical matter that means that nearly all victims will be well-intended people who slipped up once and got caught. OR people who are targeted for some reason: If animal control wants to find a violation, they will find one.
Most violators of the law will shrug their shoulders and abandon the dog.
It's only the BEST breeders who are at risk from such bills. There'll still be plenty of dogs and plenty of business for pet sitters.
As a practical matter this is dog population control by doubling the risk that the dog is struck by lightning. Yes, spay-neuter will happen, but it'll be on a semi-random basis, too rare to have an effect on eproductive statistics. The largest effect will be due to increased abandonment in the first year or two by people who believe that the law actually requires spay-neuter of all pets and who cannot afford that.
You have to wonder about legislators who cannot think through how such a law would work. How can they possibly figure out a state budget?
Oh -- wait ...