This can be such a controversial, emotional topic.
I have had far more dogs from breeders than rescues but have had both. Everyone has their reason for preferring one or the other but IMO that's all it is, someone's personal ideas about the subject which may or may not reflect reality or mesh with someone else's personal ideas. I don't see why anyone should feel guilty about where they choose to get their dog, it's your dog and you should get the dog you really want and that best suits you.
I had a well bred GSD who had temperament issues and didn't live to see his third birthday. One of my other well bred (but unrelated) GSDs lived into old age and was always very healthy and had an excellent temperament but had several siblings with serious health issues and her mother developed a serious health issues when she was middle aged. I have two well bred Belgians who developed more minor but definitely genetic health issues (a mother and daughter). My pound rescue mixed breed had a more minor genetic health issue too. Dogs are living creatures and stuff happens. Sometimes genetics work in your favor and sometimes they don't. Going to a breeder who health tests can definitely weigh the odds in your favor against diseases in that breed that are able to be tested for. Diseases that are not able to be tested for though...breeders do what they can with the knowledge they have at the time of the breeding but those problems are a lot trickier. And certainly in some breeds where there's widespread serious health issues and/or a generally short life expectancy, a random bred dog from a shelter is probably going to be healthier than a well bred purebred
of that breed. Otherwise, I have known purebreds (well bred and not) who lived to be very, very old and were extremely healthy. I have known mixed breeds who lived to be very, very old and were extremely healthy. And dogs of both who did not and were not.
Wanting a dog with a certain temperament/character are big reasons to choose a certain breed and a certain breeder for sure. That isn't to say you couldn't find what you were looking for in a rescue but the more specific the needs are, the harder it is especially in the more popular pet bred breeds where there's a big difference between the pet type and more carefully bred types. And of course, in some breeds finding a rescue dog is difficult and that isn't even taking into account temperament or age or suitability for you. There's generally fewer than a dozen Groenendael in rescue each year. And many of those dogs are older and most are best suited as companions.That goes for Tervs too. And you'd be hard pressed to find a Laeken in rescue anywhere. Same with PyrSheps.
The two rescue dogs in this household are just as good as the well bred dogs in terms of structure, drive and suitability for sports. Ziggy was adopted from a shelter and is very intense and crazy and driven. If I were to look for a well bred Cardi, I'd want one like him. His structure isn't perfect but he's 10 and still extremely sound, which I think is the best you can ask for in any dog. Roust is...well Roust. He does have an issue with strangers touching him but then, so does my friend's well bred Mal. He's crazy driven, fearless and almost too willing when it comes to trying any sport I've asked him to try. In every day life , he's a typical doofy, dorky, overly devoted Belgian boy. Mals like him aren't all that uncommon in Mal rescue, in fact most of his litter ended up there. That doesn't mean people should feel guilty for wanting a Mal from a good breeder though, who carefully raises and socializes and imprints and really gets to know their puppies before they go to their new homes. Like I said, for me "because that's what I want for my next dog" is a good enough reason for choosing to go to a breeder over a rescue.
I support both rescuing and breeding, I know people who will never have a dog from a breeder and people who will never have a rescue. I also know plenty of people who have been on one side or another of the "never have a _______" debate who...well now have what they never would have
For me personally, rescues don't tend to be as ideal because I strongly prefer raising puppies and strongly prefer to decide myself when and if dogs of mine are altered. And my involvement in dog has long been on the buying from a breeder/breeding my own side of things since I am also involved in showing and interested in having breeding quality dogs. I feel more good, educated breeders are needed, especially in my lower number breed. In terms of "overpopulation", I think it's an issue in certain pockets of the country and/or with certain breeds. Here, we have too many pit bulls. The pounds/shelters have an abundance of pits and pit mixes all the time and they are not exactly an easy breed to fit into a lot of pet homes. I don't know what the answer is for pit bulls and I don't pretend to. But I also don't see how what dogs I choose to bring into my home would have any effect on homeless pit bulls at my county pound.