Boy, Plainfieldpoultry, did you ever run into a buzzsaw!
In defense of what you said, I am familiar with the place you're coming from: a background in breeding and showing tropical fish. In fact. I'm sure we have probably crossed paths sometime in the 70's and 80's when I was chairman of the American Cichlid Association's BOT and judging fish shows in the NY/NJ/CT area.
For those that aren't up on breeding of tropical fish, especially Rift Lake African species, there was, and still is, a great deal of crossbreeding of species that not only diluted the original imported species but ruined the hobby with a mass of mutts. For those showing fish--and these people can be very serious about this phase of the hobby--this was a real concern. This also caused a great deal of debate and consternation in the ACA, which has condemned and pretty much banned the practice--although if you buy them from your local fishshop there is no guarantee what you're getting is the "real" thing. I can well expect this can produce the same kind of thing if one is into showing chickens.
That being said, the big difference between tropical fish and chickens lies in the fact that tropical fish are show animals, period. Whether you want them as part of your decor or are hauling them hither and yon across the country to amass trophies. Aside from that, the only other purpose is for one to be able to breed and sell to others that want them. If you're doing this and want to be ethical about it, you will keep pure lines going. (This can also be an expensive obsession--I know from whence I speak having had over 2000 gallons of water in aquariums in my fishroom when I was seriously breeding and selling them.)
Whereas chickens can be shown, seriously so, most keep them for pets and/or eggs/meat. This being the case, the main purpose for breeding is going to be to produce better eggs or meat and if this can be done by cross-breeding, so be it. Most are concerned with increasing their flock, not selling animals to be shown. If one is into show animals then it is up to the bodies governing them,i.e. APA and ALBC, to make sure of the lineage of those birds being shown. For the average BYC'er this is not going to be a problem nor is it something that is within the scope of those posting here be worrying about controlling.
I might add that, if one has mutts and either sells or otherwise disposes of them that they inform the new owners of the fact. It would be wrong not to do so.