I don't agree with this sentence, because the zoo is the gathering place of animals in captivity. Or animals live in the area that can control. The goal is to study the research. Conservation of rare animals as well as published to the public. Which might have to admission or value activities. But to no purpose to trade or business circus animals.
For example. The zoo opened to the green, intended to build a zoo is to conserve wildlife conservation breeding animals. It also creates a balance of natural system. To provide knowledge on learning and education, research, research and recreation. To make a place for rest, recreation, etc.
So the zoo is not a place that cruel.