I'm ambivalent about it. Polar bears routinely starve in the wild. That can't be fun. I probably look at it as a necessary social evil. We want the people to be able to actually see & slightly interact with the animals of the planet, that is a good & useful accommodation.
They also breed endangered species, so if you ever hear that a species is "extinct in the wild", then the last remaining members of the species are probably being kept in zoos, and everything is being done to make it possible for them to reproduce in captivity. Sometimes it works, in my own backyard the California Condor was on the verge of extinction, and the last 20-odd condors were taken into captivity and allowed to breed in safety, and I saw them at the San Diego Zoo Animal Park adjunct. A decade or two I started seeing them in the wild, they were released and they went back to being condors.
British zookeeper and animal collector Gerald Durrell was the first to have the idea of using zoos to breed endangered species, the practice has spread and good thing too. Some captive breeding is necessary, and zoos are the ones that are doing it.
I love Cheetahs and they are fast approaching extinction in the wild. We have several at the Cincinnati Zoo and they have a large area where they can run.
Once upon a time, I thought about getting a canary as a pet. But I couldn't abide the idea that the bird would be cooped up in a cage. I just don't think it's fair to the bird.