I am not a fan of allowing mutations that would normally "not" survive in nature.
As to goldfish, because they are the product of thousands of years of modification, created to be seen from above, with thousands of years of tradition, I can give them a bit of a pass. And they are basically carp.
But I believe the realization and knowledge that creating mutants with obvious health issues in the modern world seems less than desirable.
And as you may have guessed I am a cichlid purist, whether short bodied mutations or hybrids, or even color modifications like black angels, electric blue whatevers, or even albinos, I don't want to have them in my tanks.