And that is one interpretation of what the "point of most zoo's existences" is. There are also many other arguments here, for instance I'd say it is much more important to maintain strong education and community engagement programs, investing in research efforts, and providing resources (both economic and otherwise) to conservation efforts. Conservation programs are great, but it's much easier for captive rearing programs to happen in places closer to an animal's native range (e.g., for US zoos, head start programs for native turtles, reintroduction programs with red wolves, burying beetles, and hellbenders, etc.). In particular, it's important to have frequent founders imported into any captive program with the intent of reintroduction, as it only takes one or two generations for the loss of subtle, yet behaviorally important traits- such as antipredator strategies, that would turn almost any reintroduction effort into a failure.