Salt water fish? they don't need your tank to survive and be happy. they have the ocean and we kidnape them from their home and claim self righteousness?
Please don't put words in my mouth. It's all too familiar tactics for scoring points in debates. Go back and check every single word I typed then see how I applied "moral righteousness" in this case.
Indeed, humans have fallen natures, and I do not deny my own tendency to sin. In this case, you did raise a very interesting question:
We kidnap an animal from their natural surrounding then have them subjected to our pleasure, how can we justify our behavior?
I can't answer the question for you, but I will answer the question for myself. Being a person who has been attracted to fish at very young age, it has been my desire to have close contact with them. Over the decades as my knowledge, skills, understanding, compassion, and financial means have increased, my approach to my hobby evolved accordingly. To me, hobbyists can be a tremendous resource to educate general public to preserve the nature. Thanks to the development of the modern economy and technology, the advancement of reef/fish understanding is no longer the privilege to biologists. We as hobbyists can also contribute to this field, at the expense of "kidnapping animals from their natural habitat".
At the end of day, we all need to justify our actions before we comfortably go to bed, without internal conflicts. If you don't feel right about doing certain things, you shouldn't keep doing them. It's simply for the sake of your mental health.