So, you are not really discussing ownership of pedigree dogs. You are discussing bad breeding practices employed by only some breeders of only some breeds.

If I may restate your question in a way that clarifies the root issue:

Is it morally wrong to engage in or financially support breeding practices that, whether through ignorance, use of gene pools with inadequate depth, or negligence, produce genetically inferior dogs, particularly dogs with genetic health problems.

Does this restatement address your concerns?

If so, the restatement demonstrates that your problem is not actually with pedigrees or the general enterprise of breeding pedigreed animals, nor of purchasing them. Your problem is really that many breeders' priorities, resources, or skills are inadequate to engage in effective animal husbandry.

Consider what is at the root of these dogs with health issues.

The older breeds tend to be from stock that was skillfully bred for task-related qualities that are of great advantage both to the owners and to the dogs. These breed groups-retrievers, shepherds, mastiffs, spaniels, hounds, terriers have many breeds that continue to be bred for the ORIGINAL qualities, and by and large, they are healthy dogs BECAUSE of the maintenance of their pedigrees. The only semi-common problem is hip dysplasia in large breeds.

Most of the problems you are concerned with appear only with dogs bred specifically for show, regardless of the original purpose of the breed. There are two main problems that produce dogs with the health and behavior disorders.

1 - Often when selecting for qualities like color or markings, a breeder inadvertently selects out for genetically related (on the same chromosome) negative qualities. This focus on incidental phenotypes may also breed out of the dogs the very positive qualities (temperament, strength, intelligence, etc.) that were the goals of the original husbandry that developed the breed. This is especially common when breeding for miniature and teacup breeds, for particularly uncommon markings, and for all white variations of otherwise varicolored dogs.

2 - Some breeders draw from too small a gene pool. Sometimes this is because they do not have enough dogs in their program, and sometimes this is because their dogs all come from the same bloodlines, and they do not know it. The problem of working from too small a gene pool is that while it compounds positive traits, it also compounds negative recessives.

Recessive genotypes only present as phenotypes when the dog inherits the same genetic trait from both parents. As a result, rare recessive traits may be invisibly, and harmlessly passed on in a suitably large population, but only appear when the breeding population gets too small or too closely related. (This is one of the reasons that the policy of neutering/spaying all dogs that come into shelters is ultimately disastrous to the American canine gene pool.)

These two factors are easily avoidable when breeding pedigreed dogs, and there are several breeds that avoid these issues, partially because of how common they are (large gene pool) and partially because of how popular the original traits are with the people who judge the dogs in dog shows, as well as those who buy the dogs. German shepherds, Australian shepherds, large terrier breeds (pit bulls, etc.), Labrador retrievers, golden retrievers, chows, standard poodles, and most hounds are bred for pedigree very successfully, and generally produce very healthy animals.

On the other hand, the new breeds, usually miniaturized versions of the old breeds, are often screwed up because dog show organizations and breeders selected target traits poorly, did not cull and cross lines often enough, and drew from far too shallow a gene pool.

This would imply that buying a "miniature" anything is likely to be ethically suspect, pedigree or not.

It would also indicate that buying most large breed dogs with pedigrees is most likely to be ethical sound.