Frankly, I believe people derive pleasure from their fish from not only appearance, but especially from behavior. I take great joy seeing my convicts herd their fry around the tank while defending them against my descending fingers as I squirt bbshrimp into their feeding areas. I also enjoy seeing my friend's moray eel dart out, strike, and consume live fish. Isn't the joy of an aquarist to recreate conditions, so that the natural behavior of their animals are expressed? Now, if you have problems with predatory fish and people deriving pleasure from observing that behavior, then that's your perspective and value judgement, but it is not necessarily more moral or ethical than mine and I'm sure others like me on this forum. In my opinion, of course...