Something else about the "hybrid" and actually creating a new "strain". In the case of the mule it is right there, the two animals breed and you have a new species or strain. In the case of fish however, there are very few that are pure so creating a "strain" can be very difficult. It can take many generation and many years to create a specific charcateristic that is always gotten after every breeding of the parents. A mix of characterisitcs like we got with platties, swords, mollies and other fish is just crossbreeding and not a strain.
I hope that helps to explain it a little. It is really in depth and if you really want to know all the symantics I will try to find my genetics research book and explain all the boring details.
As for the morality, it is simple. A new strain or hybridization is frowned apon by most. The actual hybridizing of a fish into something that can survive, is not deformed, and is easily kept in our aquariums, I have no problem with. The genetic abhorations is where you find the most discension in the hobby. Fish that are deformed is the biggest one. I don't remember the full name but I think it is a parrot that is so deformed from hybridization that it can't completely close it's mouth and can't eat like a normal fish. This is where the negativity comes from and most won't even care if you intend to do it right. At least most initial reactions come across that way.
Is a little like a hairless dog or cat. The breeder knows that the animal will never sirvive outside on it's own but they breed them anyway. People who buy them know they will never survive outside on their own but they buy them anyway. Where morailty comes in and it becomes truely wrong, I don't know because hybrids are aquarium animals and bred to be just that. Hairless pets are bred to be pets and never returned to the wild.
All I can say is do your research if you want to try it and even if you don't and form your own opinion. An educated decision even if based on biased information is at least educated.
BTW, Welcome to the forum. Hope you enjoy the club and have a little fun at the same time. Oh and maybe learn something