The issue with the argument that shelters are full of pets so you shouldn't breed for pets is a bit off base. It assume that people looking for pets are open to taking a dog of any type, any age. And that there are enough pet quality puppies from working/show/sport breeders in the popular breeds to meet the need of people looking for pets of a certain breed. I will use GSDs as an example. A person who just loves GSDs wants a nice puppy for a pet. They look into breeders in their area. They are turned off by the show breeders dogs because of the structure. They are turned off of the working bred dogs because of price and maybe are told those dogs would be too much for them. So what's left? Pet breeders and rescue/shelters. One could argue there are plenty of GSDs in rescue, so that would be the obvious choice. But there's not many GSD puppies in rescue and knowing if a puppy at a shelter is actually a GSD puppy or not can be tricky.
This is the person that pet breeding is for, not people like most who post on this forum. It is for a pet owner who likes a specific type of dog and wants a puppy. Not everyone can justify spending $1000-4000 on a puppy from the best of the best pedigree because having the best of the best pedigree doesn't matter to most pet owners. Even if they could, there just aren't enough pet quality dogs being produced by show/sport/working breeders. This is especially true in toy breeds, where 1-3 puppies is about all you get in a litter.
When I was a little kid, before getting into dogs my parents bought their dogs out of the newspaper and what we got depended on what was for sale and what sounded good. My parents got the puppy, then bought the breed book and read up on the breed. And such a story makes dog people cringe but really, my parents had pretty low expectations for behavior and were committed to the dog for life. And that went for any dog we got. When I got my own first dog, we went to the pound and picked out a Beagle mix because my parents didn't want another dog that would be too big. The Beagle mix grew up to be 85lbs and had fear reactivity/aggression issues for his first 3 years and still, he was never at risk of losing his home. My first purebred dog was a Collie my parents bought for me as a teen from a pet breeder for $150 (breeder did health test but didn't compete in anything and openly bred for pets) and he was a wonderful dog. I looked and looked at "good" breeders when he died to find another dog with as good of a temperament as he had but had no luck at all.
Also while it might not seem like it, ending all pet breeding of all breeds might not be the best thing for the breed because it will diminish the gene pool. I know of a group of breeders in one toy breed who went to a commercial breeder for dogs because it was found that this breeder had some of the only dogs left in the breed who were free of a popular sire, including many pet bred dogs. The dogs they got were not "low quality" either. They were able to finish at least one of the dogs and many of the puppies of the dogs were show quality. But even if they weren't show quality, it was a worthwhile project to preserve a line which would have otherwise been lost.
There is no one easy answer to the subject of who should breed, which dogs should be bred and where everyone should be getting their next dog or puppy.