Given that we go through the trouble of sourcing net caught fish, or aquacultured fish. Then quarantine them to clear them of disease and parasites, as well as condition them to their new environment. I think this hobby can be very ethical. There are people that don't care where their fish come from, as long as it's the cheapest price they can find in the solar system. I consider these customers more ethically ignorant. Then there's the hobbyist that procures their fish from quality sources, which already go through a quarantine process. They'll pay more knowing that this fish was cared for better in the supply chain.
I've evolved through this hobby a lot since 2005. I started out with a 10 gallon tank with crushed coral, mandarin, and some sun corals. Whoops! Now I'm loosing sleep at night as I try to raise angelfish, dottybacks, blennies, and sea urchins. I've turned my hobby into a business to provide ethical and sustainable options to everyone.
I also try to raise monarch butterflies in the summer from eggs to offset the butterflies that I've hit with my car.