The logic used in the argument that for every puppy/dog bought, one is killing another, has always amazed me in how far it reaches and is based on assumptions. First it assumes that if the person did not go to a breeder, they would have gone and saved a life from the shelter, which is not necessarily true. Some would rather have a dog whose background they know and who has been bred specifically to a purpose to fit their lifestyle best, and would forgo getting a dog at all if they could not pursue that course.

You could really make reaching assumptions and accusations like that all day long about a great many things, i.e., because I adopted my dogs when they were cute puppies and highly adoptable, I condemned older, less wanted dogs to die. You could even carry it further and further.

Anyone who decides they don't wish to own a dog at all is killing a dog in a shelter.

Anyone who decides they prefer cats or other pet types are killing a dog in a shelter.

Anyone who only rescues one dog when they have the financial ability to take more is killing a dog.

If one goes to a breed rescue or no kill shelter, they are killing a dog in a high kill shelter.

The crux of the problem is not who adopts what and where, but irresponsible breedings: Those who dump litter after litter of unwanted dogs simply because they don't care to spay/neuter their dog. Puppy mills that "farm" dogs for pet shops with no care at all to their conditions, temperament, and proper care, they pour hundreds and thousands of dogs into picture, many with a myriad of health and temperament problems that land them in shelters and often on the euthanasia table. It is those people responsible for all the lives lost and dogs languishing in shelters. It is to them you could truthfully say "you are responsible for the suffering and deaths of dogs in shelters."