Look, you can argue till the cows come home, but it is a scientific fact that mongrels and more diversely mated dogs have better health. They have fewer genetic health issues and tend to live longer. Some example studies below.
Please show me the studies where pedigree and selective breeding by your so called responsible breeders has improved the canine species over the long run.
^P.D. McGreevy & W.F. Nicholas, Some Practical Solutions to Welfare Problems in Pedigree Dog Breeding, Animal Welfare, 1999, Vol 8, 329-331 "Hybrids have a far lower chance of exhibiting the disorders that are common with the parental breeds. Their genetic health will be substantially higher." (P338)
A. Egenvall, B.N. Bonnett, P. Olson, Ã…. Hedhammar,Gender, age, breed and distribution of morbidity and mortality in insured dogs in Sweden during 1995 and 1996, The Veterinary Record, 29/4/2000, p. 519-57
B.N. Bonnett, A. Egenvall, P. Olson, Ã…. Hedhammar, Mortality in Swedish dogs: rates and causes of death in various breeds, The Veterinary Record, 12/7/1997, S. 40 - 44) ?Mongrels were consistently in the low risk category? (S. 41)
H.F. Proschofsky et al, Mortality of purebred and mixed breed dogs in Denmark, Preventive Veterinary Medicine, 2003, 58, 53-74 "Higher average longevity of mixed breed dogs (grouped together). Age at death mixed breeds (Q1 Q2 Q3 mixed breeds 8,11,13, purebreds 6, 10, 12)"