This is a tough question for me too. My son was obsessed with animals as a child. Zoos were one of his very favorite places to visit- -the San Diego Zoo was a trip we talked about making often after learning about it in a book we read (nearly every single night for six months). We were fortunate, I believe, in that we were able to visit many exceptional zoos: The Fort Wayne Children's Zoo, The Louisville Zoo, The Indianapolis Zoo, The Toledo Zoo, The Cincinnati Zoo, and The National Zoo. We finally made it to The San Diego Zoo six years ago. (I saved a fortune in souvenirs taking my son as an adult! haha) These zoos all have a lot in common. There is very ample space for the animals, most of the exhibits are open air, and there is a larger than normal border between the animals and the people. I also noted that the zookeepers gave the animals in these zoos breaks from being on display.
If the mission statements of these zoos listed are to be believed, their intent is to preserve life, offer protection, educate, and support breeding programs so we do not lose valuable species. And I support this.
However, zoos like the one in the book (in Little Rock) that are crowded among other problems- -and seem to be more for the enjoyment of people than improving the lives of the animals, bother me. For the most part, I see zoos as one potentially responsible solution to all the irresponsible actions humans have taken against animals and their habitats.