What's wrong with breeding MUTTS?!?!?

Mutts are great and as others have said, if it were not for people breeding mutts than I would not have gotten the dogs I did from a shelter. But what is WRONG with intentionally breeding mutts? The same thing that is wrong with irresponsible purbred breeders. Without the research and genetic testing you are allowing puppies to be born carrying genetic defects and diseases that may not be obvious to the breeder or the seller, but it will be obvious to the owner, the vet and the dog later. And if that mutt breeds with another mutt .... and so on and so on. I had a corgi mix with periodontal disease (genetic), my sister had a lab mix that had to be put down at 6 months due to hip dysplasia (genetic), a friend that had to have several eye surgeries on her bet hound mix (genetic) ... I am sure there are hundred of stories out there, if you know what genetic defects run in which breeds. A good breeder does genetic testing to keep these genes from being bred into their line. Aside from that, how do you know how responsible a mutt breeder is? There are standard questions you would ask a breeder to determine if they are a responsible breeder or not. What would you ask a mutt breeder? A responsible breeder can show you the geneology of their breeding line, what would a mutt breeder show you? How would you know which mutt breeders provide good medical care to their breeding dog and their puppies and which ones just put them in a room and have at it? I am sure there are a lot of answers to this question. That is just what comes to mind at the moment.