To begin with, animals kept in small enclosure or cages become unsettled and stressed. Once there was a gorilla named Jabari locked in a zoo enclosure, was trying to escape by trying to jump over the walls and moats of his enclosure, only to be fatally shot by police. Witnesses later confessed that teenagers had been taunting and mocking him by throwing rocks at him. This is unfair and unacceptable.
On the other hand, animals in zoos are fed at certain times and given food, that strips them of having the skills they used to have to hunt and defend for themselves. They also lose the ability to identify which animals are predators to them. The animals end up depending on man to feed them and lose interest in looking for it themselves. Animals can develop a disorder called zoochosis (repetitive behaviour pattern) which means that they do the exact same thing everyday, like walk around in the same spot everyday because they don’t have enough room to walk around.
Furthermore, animals are kept in captivity just for our amusement. They are mostly beaten, chained and tortured just to train them for our enjoyment. For an example, there are sports like bullfighting, where bulls are drugged to weaken them so that they don’t stand a chance against the human they’re versing. In sports like horse, greyhound and dog - sled racing, they’re drugged to avoid sickness and injuries and are intentionally forced to race. In between races they are kept in confined cages where they don’t have space to walk or even turn around. When these animals don’t win they end up being put down (euthanized), shot, sold or laboratories for experiments or sent to slaughterhouses,
I hope i have convinced you that animals are living creatures, they should be set a little bit free, and treated with respect. There are always other remedies of training them, or keeping animals safe. In the end, we all belong to animal kingdom.