Well, people might see them as a threat or something else in their eyes. However, they still deserve equality like the humans have. They are also living things that should have the same rights, having freedom and do their own things which we human beings do. It is cruel to lock them up in a cage, instead of letting them to live their way they want in the wildlife. Some might argue that it is use for wildlife conservation, preventing endangered species from going extinct. But, in fact, the percentage of endangered species in most zoos is probably a small 3-5%? So, why cage them when their lives could probably be better in nature?