
They're obviously enjoying themselves, using you as a 'punchbag'. The problem is that you entered into the argument using your personal experiences and that's given them an opportunity to personally attack you and use your examples to back their arguments (supposedly). Next time (if there is one) try to keep the information objective and generic using facts and figures that they can't argue against.
Strictly speaking one of them is correct in saying that pedigrees have evolved through human intervention playing around with mixing breeds. So, at what point does the mixing of genetics result in a breed? In other words, how many generations of breeding Labrador x Poodles would you need to be able to call the crossbreed a pedigree? If you know the answer to that one you have addressed the mongrel comments on the thread. I haven't got a clue to the answer. Breeds have been bred to suit man's work needs in a variety of domesticated animals i.e. cows have been bred selectively to produce certain milk, the Fresian is most commonly used for milk because it yields higher quantities than other breeds; chickens have been bred selectively to produce eggs with harder shells so that they don't break so easily when they roll down the chutes in the battery farms (actually, I don't know if that is true, someone told me this is why eggs take 4 minutes to boil instead of 3 which was the standard time when I was a kid). :-) Anyway, point is that dogs are just another domesticated animal and used to either work in a variety of occupations or as companions.
If they then go on about breed defects then I would just simply say that if it is
proven that breeds are suffering because of breed standards then of course this should be investigated properly and adjustments made. That would have to shut them up. Whatever they come back at you with you've just answered and need say no more.
At the end of it all the main point is that breeders who do try to breed responsibly, follow breed standards as set out by a governing body. They research and study the breeds and prospective breeding dogs before embarking on litters. Responsible breeders pay out for a variety of health checks in order to avoid potential health problems. Unfortunately, it is the back street breeders who are perpetuating the health problems by not researching pedigrees for good selection or health checking their breeding dogs. It's those peope who make the big profits, not the responsible breeder.