The problem with that, is that I really have heard it all before. It's not like I've never spoken to a breeder before. It's not like I don't know what their position is. I even read a good portion of the thread it was recommended I read, though it seems to be unbelievable to Lakl that anyone could read that thread, and still have their own opinion that differs.
Arguing with a breeder about the basic concept of breed purity, is like trying to get a Christian to renounce Christ, and convert to Judaism. Their entire world view is centered around the idea that breed purity is a desirable trait. All that will happen, is you will end up mired in the minutia of dogma. It doesn't go anywhere, and no one learns anything, because when it really comes down to it, it is a faith-based position, leaning on tradition, and adopting the parts of modern science that support their world view, while rejecting, ignoring, or being impossibly hyper-critical of anything that causes problems with their world view.
There are entire websites devoted to this argument, and there are many scholarly papers by both geneticists and breeders addressing the subject. There is nothing any breeder in any forum can say, to get around the simple scientific evidence that biodiversity is advantageous to a species. Any argument that tries to support improving the health of a species, by limiting biodiversity, will necessarily include rationalizations and a priori assumptions that have to be taken on faith. That isn't some random opinion I just happen to have, that is the current state of a modern understanding of genetics. If you maintain a small gene pool, and practice selective breeding only within that limited gene pool, you are practicing damage control, not improving the species. That is what genetics has to say about a lack of biodiversity.
Arguing with breeders about breed purity, is no more productive or beneficial to me, than it would be to go to some audiophile website, and argue about $10,000 stereo cables that supposedly improve sound, or some free energy website to argue about perpetual motion machines, or any other group of people who earnestly and wholeheartedly believe in something that is scientifically questionable, to the point of being highly unlikely to be true. I don't have to hear someone's subjective arguments, to look over the research, see the experiments, and read the results. That, to me, speaks a lot louder than someone's passionate defense that they love their dogs, and have been doing this for 30 years, with what they self-assess as good results.
What is a worthwhile conversation, and all I was doing initially, is to talk to the person who isn't sure if they should buy that $10,000 audio cable, and let them know that there is no scientific basis for a special cable making something sound better. Talking to the people who already bought the cable, is a waste of time, because their $10,000 investment, will cause them to skew their perspective.