Animals in enclosures - Did this ever cross our mind?

In the human society, all tend to respect and give hero / heroine treatment to someone who endures pain for others benefit. Showing gratitude like that is a great human quality. But attitude is quite discriminatory when it comes to animals that are imprisoned in small enclosures in public and private zoos, circuses and other scientific and entertainment ventures for humans comfort. For instance an African lion that would roam around a territory of 20-400 sq km is, in most cases, confined to a few square meters during its whole life for our joy. Did this ever cross our mind when we enjoy watching them - glossy coats, bright rainbow coloured feathers, piercing or sleepy eyes, feeding, social interactions etc?