I guess I look at it this way, there is no way I would give any dog to someone I did not think would give them a good home.
I will say that again, no dog from 8 weeks old to fully mature is going to go with anyone I do not fully believe will give them a good home and a good life.
My keeping my retired bitches isn't doing them any favors. I am keeping them because I am too selfish to place them where they will be loved on by a family for the rest of their lives. There is nothing heroic in that. Yes, I do love them, and they know only me, and as far as any dog is capable of it, they love me. But if I were to place them with someone else, they would learn the new people and love them too.
Every dog I keep means that all of my dogs get a little bit less. The puppies and young bitches require more, they will get more, the older ones require less, and yes, they could have a much better existence in the eyes of people here being in a home with one other dog, or no other dogs, and maybe more people.
The same is true if you do a test breeding and the puppies come out with stripes. Ooops, we have the striped gene going on here, Let's neuter this boy and girl and find them awesome homes. That way those dogs I have, the dogs I bring in or keep from other litters to replace these dogs in my program, will have that much more of me, while the dogs that throw striped puppies will have an awesome life with people who love only them. It is a win-win solution for everyone.
And the striped puppies, there will always be people willing to take puppies that are rare, like blue or liver or brindle or panda, some like whites, blacks, sables, bi-colors, coats, and whether or not these are rare or off-color, or not, there is nothing wrong with them going to homes. But if you do not want to produce certain traits, and especially if those traits are out of standard, it makes sense to pull the dog from your program, and to sell the puppies. If they are out of standard, it may be best to alter the dogs before placing them, so they are not used by unscrupulous breeders who will breed them specifically for those traits, for as much as they can make out of them. As a breed guardian, that is really not hypocritical.
But if the test breeding produces less desirable traits, or health problems, well, the choices are to place the puppies in homes that will provide feedback and understand the purpose of the breeding and possible issues. I think that it is not necessarily unethical to do such a breeding, so that you know. Some genetics are cut and dried, some are not so, and sometimes we know what lines have what issues because of test breedings and what they produced.