Zoos teach young people about animals, which can help fuel interest in conservation. They also serve as rescue and rehabilitation areas. Zoos gives cities a valuable tourist attraction as well.
People living in urban and suburban areas rarely see animals aside from birds. Even people who live in rural areas only see a small subset of the species on the planet. Zoos give people a place to explore the diversity of animal life on Earth, and many people fondly remember their first trips to the zoo as children.
Many zoos also perform a variety of rescue and rehabilitation services, and they are at the forefront of the conservation effort. Many animals bred by zoos are endangered or even close to extinction, and some would no longer exist without zoos. While introducing animals into the environment is challenging, zoos have done so successfully in the past.
Zoos are large and somewhat expensive to maintain, but they provide a valuable tourist attraction for cities. A zoo can attract people from hundreds of miles away, and those who lobby to have a zoo constructed argue that they are living museums. Residents of Atlanta and San Diego point to their zoos when explaining some of the top attractions in their cities.