First off, I think we need to differentiate between a service dog, meaning a dog trained to assist a human with a disability, and a specialized working dog, meaning a dog that is meant to perform a highly specific task or set of tasks. The former can be many dog breeds, because instinct is less important than general intelligence and trainability. The latter often requires specific bred in instincts to properly perform its task.
Service dogs, as mentioned, really do not require a specific instinct, and I would argue that a general lack of specific dog instincts is preferable. For example, my buddy's Pointer would make a uniquely terrible service dog, because the second he sees a bird that is all he can focus on.
To keep focused on that Pointer, his instinct for tracking birds makes him an ideal working dog, because he naturally has a desire to chase down birds and has the requisite size to carry large ones back to his owner. Could you train a dog without that instinct to do his job? I mean, maybe, but there's a reason that humans have spent thousands of years developing breeds for specific tasks. Because it works.
Similarly, there's a reason why almost all police and military dogs are either German Shepherds or Belgian Malinois. These dogs require impeccable breeding due to the inherently dangerous nature of what they do, and these breeds also have the size, strength, intelligence, and inbred loyalty necessary to perform their work. A poorly bred dog trained to attack and subdue could turn on its owner.
And I think blaming all breeder for the negligent actions of some breeders, along with the dog owners who don't properly care for or fix their dogs, is silly. If you do your part and don't buy from puppy mills or breeders who produce dozens of litters a year (I always look for ones who only produce a handful of litters a year, and who don't force single dogs to have multiple litters over short periods of time), and if you spay/neuter your dogs, you're part of the solution, not the problem.