That is merely mans rationalization of this injustice.
The wild is where all animals have evolved to live in and belong to an ecological chain. For better or worse, the animal is most satisfied and content when it functions within its own natural environment, not some artificial one which poorly replicates it for the appeasement of human folly. Disturbing it sends a rippling effect of repercussions throughout the entire animal community. Man has tampered too much with the natural systematical order of things, causing havoc everywhere.
The natural habitat is where an animal is comfortable and most at home, not in some confined area where they're guaranteed a meal when made to perform. I'm sure you think the circus is a great place for an elephant as well. The treatment of elephants in a circus is a real travesty of animal life.