Thomas, contrary to popular belief, there is no hybrid vigor when mixing two breeds of the same species. In addition, it is people who breed purebred dogs who health test their animals and select their breeding stock with as much care as they possibly can muster. Many, if not most, hobby/show breeders breed to improve the breed that they have selected to work with. With few exceptions, the people who toss two breeds together to label with a "cute" name are just in it for the money.
I'm not saying that responsible crossbreeding cannot occur. Lurchers are crossbreeds with a purpose, border jacks are not (for example). When the Alaskan Klee Kai was under development, a lot of mixing occurred. When the "Labradoodle" experiment was going on in Australia, there was a lot of mixing going on. But the those people were breeding with an intended goal in mind--and now that the Labradoodle experiment has failed, I'm not sure why people are continuing the effort except to make designer dogs. Call me crazy, but with around 500 known breeds world-wide, I'm not sure why we need to mix breeds to find an animal that will fill a niche for everyone.
Edited to add
Quote:
Because they buy papers from "registries" that will register a Himalayan cat as a Pekingese as long as the name, the amount, and the signature on the check are all correct. No legitimate registry will register a mixed breed. Heck, they won't even give a mixed breed a listing number if the dog is not neutered.