Do zoos serve a useful purpose or are they unfair to animals?

During the last few years there has been noticed a great development of zoos. Some people think that such places are entertaining or even needed. However in my opinion zoos should be banned for numerous reasons.
The first argument against zoos, which I would like to present, is that in fact in most cases animals are kept there against their nature. Nowadays people are used to keeping animals at home, though these are just a few species and they have been domesticated for centuries. Most of us usually do not see the difference between these animals and the other ones, which have always been wild and have lived on the open ground. Because of our interference in animals' life and habits, some of them like tiger, lion or elephant may became completely baffled. That may later provoke a change in ecosystem, which can have terrible effects like extinction of many wild species.
Secondly, I would like to emphasis the aspect of entertainment. Is zoo really an attraction for people? To be true I muse that adults are not really interested in watching animals, which they may read or see a film about. Adults usually assume that a zoo may entertain their children. In fact such a trip is attractive for most children only because of colourful stickers, ice cream or slides proposed by zoos.
Lastly I would like to add that zoos may also spoil colossal our fragility and morality. In my opinion if we call ourselves "humanitarians", civilised and cultural we should manifest against zoos, because what may we see in zoo? We can not see there any animal family. We can not observe common habits of animals. Then what can we see? We may only watch poor animals in usually too small cages. Is it really normal that observing a living organism kept against its will through iron bars has become so common?
Summarising all my arguments I believe that zoos should be strictly banded and I hope that some day my wish will come true.

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