I think there is still a role for aquaria (and zoos) for educational, aesthetic, and even entertainment purposes.  But times change.  Now it is so easy to see real whales in the wild and it is so much better to see them there when they obviously don't thrive in captivity.  150 years ago people used to collect birds, stuff them and put them in glass cases to appreciate in their yards. Now large numbers of people enjoy watching and photographing birds or have bird feeders in their home.  The Monterey Aquarium is a  wonderful example of what an aquarium can do and can be!