A couple of months ago, there was a huge heated discussion amongst the breeders on the Collie list about this very
subject of merle to merle breedings ... In some rare cases, they felt that the small risk was worth improving the breed overall. If any of the Double Dilutes had health issues, they would immediately put them down. They absolutely would not sell any of these puppies.
Well, that's quite a sad and disheartening thing to hear, although I suppose I'm not too surprised. Just like Clara4457 said, breeders have made pugs and English bulldogs that can't breathe, GSD's that can barely walk, and deaf dalmatians and Australian shepherds galore.

I do not believe for one minute that a genetic cross known to create dogs with serious genetic defects "improves the breed overall" ... no more so than the hemophilia or sickle cell anemia gene improves the human race. I do not believe that breeders who intentionally do this are responsible breeders in any way, shape or form, no matter how well-known their kennel name is. Just MHO. It's very sad that the breed club is not taking a stand on this. I believe it will be to their ultimate determent ... and sadly, innocent dogs will pay the price, as usual.