Like most of these issues, I can talk until the cows come home about this topic, so I’ll narrow my scope to megafauna land mammals in zoos.
The general debate of animals in zoos is a hot one, with well thought out points on both sides. General arguments for zoos are that they provide funding for conservation (or even conservation programs and research in the zoos themselves) and they educate the public about animals they wouldn’t otherwise see. Main arguments against zoos include the concern of the well-being of the animals (especially the megafauna mammals), that the zoos are too patron-oriented in terms of both profit and experience and that perceived educational benefits are relative. Since the release of the documentary Blackfish in 2013 that revealed the woes of orca whales in captivity, people are beginning to think twice about other megafauna mammals in captivity.
I wrote a short paper last year that explored: under what conditions is it acceptable to place animals in captivity based on biology, natural environment, and conservation status, particularly concerning the polar bear.