I agree with the comments that there are good and bad breeders of all pedigree breeds and crosses, far more than decent ones in fact. Sadly, KC registration is absolutely no mark of quality, seeing as around 90% of KC registrations are from 'volume breeders', eg. puppy farmers. A proportion of the rest are from BYB's and less than desirable breeders, so you can see what a tiny proportion of KC registrations are from good, responsible and ethical breeders. Then when you further consider there are over 40,000 (each breed!) registrations of both Labradors and Golden Retrievers alone each year, both breeds which are hugely exploited by puppy farmers and BYB's you can see why the rescue situation is in such a dreadful state and so many dogs are being put to sleep each year.
Even more sadly, the KC accredited breeder scheme, which should and could be a mark of quality is nothing of the sort. Health tests are not mandatory at all and inspections of breeders are few and far between. There are no specific requirements to belong to the KC accredited breeder scheme, you needn't have even bred a litter yet and there is no upper limit to how many litters you may produce in a year. In fact, they have an 'accolade' for breeders having produced '5 or more litters' but this could be over any period of time, so say, 6 months, which is obviously not a good thing. Breeding 5 litters is something good breeders would take around 15 years to achieve. Worse still, some of those on the AB scheme are in fact, puppy farmers and BYB's. 
As was seen by the other thread, puppy farmers are extremely clever at saying what seem to be all the right things and creating a good impression for the general public. It's a huge shame that a very well documented programme a few years ago wasted time 'exposing' pedigree dog breeding instead of educating the general public on how to find a good breeder, regardless of what they were breeding or how to find a good rescue.