I agree with everyone else ... sometimes it is necessary for the survival of a species to maintain captive populations. And some zoos are VERY nice.

Also, I think people are more likely to care about and try to help save animals they have actually seen "in real life".

Actually, captive animals do not die at an earlier age than wild animals. Due to lack of predators, a steady diet, vet care, etc. captive animals ususally live much longer lives than their wild cousins.