Maddyfish, I'm with the others on this, I don't see why crossbred clownfish are a problem. I do think there can be ethical dilemmas with interspecific hybridization. However, I don't think any of those hold true here.
Reasons why interspecific hybrids are a bad idea include;
1) Rare species where all specimans left should be use to continue the species.
2) non-naturally occuring hybrids that could potentially be released into the wild and have unforeseen consequences.
3) Hybrids where the resulting offspring are deformed.
I'm sure there are more reasons, but I don't see how they apply to captive clownfish. They're not going to go back to the wild, and their lines are stable. No outward deformities have been discovered in crosses, unlike the hybrids of some species (freshwater parrotfish come to mind).
Most of these clownfish are captivebred for several generations, especially your standard ocellaris. They are already genetically different from their wild counterparts. Whether intentional or not, when you breed a species in captivity, you change it. Those that can not survive in captivity, die, those that are better suited, survive and breed. The divergent point for why some survive in captivity and some don't might be where the characteristics that would allow them to survive in the wild are a disadvantage. In that sense, if a hybrid clownfish and a "true" species are still only suited for captivity, why shouldn't hybrids be allowed?
Another reason not to worry about hybrids is the fact that species is an artificial human concept. Even among scientists, the definition of a species is often not agreed upon. And with the ability to map genomes, the definition will probably continue to change. But fish do not see species. They see animals that they are interested in breeding with or not. Many times the only thing that keeps different species from breeding is isolation, and dramatic natural environmental changes can result in a new species developing through hybridization.
I would say its not in our best interest to encourage new species/hybrids in the wild, but in out home aquariums, why not? If they're better suited to captivity, then we've made a step forward FOR the fish. And if not, they will die out just like a naturally occuring hybrid not suited for its environment.