Well I do not think that I agree with that totally. Zoos or zoological parks are the places we keep various wild animals and birds. One reason for keeping them in zoos is that they are used as a visiting place for tourist families and children. It is a memorable place for kids for sure.
Zoos are not really cruel places for the animals in one sense. The wild animals are kept in cages or in small compounds with some grass, water surrounded by walls. They are protected safely and their health is looked after carefully. They are fed good food that should keep them energetic and make them live long. Further if they live in the wild, they may get killed by injuries and by carnivores. Also, the care is taken for facilitating reproduction of the animals.
However, zoos are cruel places if viewed from another point of view. The animals are often disappointed, feel bored, have nothing to do and are tired of taking rest. Lack of any glow in their eyes and unattractive walking style show total lack of interest in living in zoos.
We need to enhance the life of wild animals in zoos. Bigger areas for their movement are to be planned. They are to be allowed to meet another harmless animals in a controlled way. Or, we can use some forests as natural protected biodiversity parks.
The care takers at zoos must be trained well and they must be honest. There are many incidents reported in newspapers often about some animal poaching and hunting illegally, for earning money in black. This must be prevented. Perhaps some games may be taught to the animals and they may be left in zoos to play with their partners of the same species.
We need to protect some species as they will become extinct in their natural habitat. Also we must make their life more interesting in some way or the other. Perhaps in future we are able to do that.