The way i see it, as long as the people who own the fish, know EXACTLY what they are doing, treat the fish properly and give it everything it needs, I'm fine with it. Aquariums and Zoos are huge conservationism centers, not only to they teach us many things, but they also captivate children who grow up to help the animals.
take Steve Erwin for example, everyone knows who he was, everyone was sad the day he died, but he did want he wanted to do, teach the world about all animals, and spread conservation, and he did a damn fine job. he owned a zoo.
And it helps aquaculture, the day i can buy a fish without having to take it out of the ecosystem is going to be a happy day. many aquariums learn how to breed species, and develop aquaculture centers for them, reducing the demand on the real world.
IMO, zoos and aquariums are good, AS LONG as they are in the right hands, and have life long, trained professionals, working with the animals.