Regarding breeding of them...
They're are technically treated as intellectual property- it's actually illegal to "intentionally" breed them.
Now, that said, who will know if you do it intentionally or not? I think they're out to stop people doing it en-masse. If you stick Danios in a tank- they're going to breed. I constantly see spawning behaviour in my tank... although, not seen any baby fish yet... presumedly the eggs get eaten by snails, shrimp and fish.
Also, the genes arn't quite "man-made"- they were taken from other organisms- and man stuck them in the danio... I think the original glo-fish had genes from Jellyfish inserted into the DNA of their fertilised eggs to make the current Glo-fish.
Ethically- it may be a gray area... I can definately see both sides.
I have a few in my Danio school- mainly because my wife liked them... although I've come to appreciate them as pretty fish.
Personally though, I think some of the regular morphs are more attractive... The Zebra, Ocelott, Leopard, Golden... etc...
Danios come in so many colours naturally- most of which are superior in appearance to Glo-Fish... (in my opinion).