I think bred lines of discus or even the glo-danios are fine. The point for most of us is not to replicate nature, but rather to create something similar to nature, but more attractive than nature. Obviously, which particular discus a person likes depends on a particular person's aestethic sense. Besides, with rare exception, none of us would know what "natural" discus or other tropical fish looked like, except by seeing them in books or aquariums. So, really, if your only opposition to an unnatural fish is that it looks unnatural, you're really saying it doesn't look like what you're used to seeing in certain unnatural settings.

As for "painted" fish, I think physically dyeing a fish is cruel and I try to avoid stores that sell them.