Justify to whom, exactly? Justify to yourself? Your peers?
Who is to say what is the standard for excellence? From a biologist's point of view, the animal would be better off in its natural habitat, for that is the standard. Or a restaurant would say that an excellent aquarium is aesthetically pleasing, regardless of the well being of its inhabitants.
My point was that we don't have to go all bleeding-heart-animal-rights-nut to understand that we are doing harm. Stress is a neurological response that can be observed. "Suffering" is an subjective emotional response to stress. Two people can undergo the same stress. One might "suffer;" the other might not.
Stress suppresses the immune system and leads to disease and premature death. Once you understand that, the question you have to ask is, are you okay with that, and why?