comparing breeds of dogs to locales is much closer than comparing breeding two separate species to mixing breeds of dog. Dogs are the same species from the tiniest little toy poodle right on up to great danes. They've just been bred out so many times that they look different. Veileds and panthers are to totally different species with different genera, and that's not the same as mixing breeds of dogs.
Panther crosses are pretty much the same thing as we would call a mutt. It doesn't take away from the looks of the animal or anything, just states a fact that it's a cross from two bloodlines. At the "pet trade level" it's a matter of personal preference as to whether you want an animal with a single lineage back to an area, or one that takes some of the best of all. Nothing better or worse, just different.