Sudhir, what you said is truth but, in my opinion, the preservation of animal species would have to be made in natural parks and not in zoos, in cages.
I love the play of light on the cage even though the subject is obscured and seem very bored :-) in captivity. Your words sooooo true!! But need I tell you this? ...it allows those far from the natural environs see them and appreciate wildlife and their conservation: http://www.usefilm.com/image/586071.html Also, for educational reasons, they serve a good purpose of safeguarding the endangered and revival of a species like tigers which have been re-populated prior to their extinction: http://www.usefilm.com/image/563871.html
If not all the above, for nature photogs like u and me who cannot get into the wild much, it gives us a chance to satisfy the primal urge to hunt or shoot..... on film / digitize / immortalize these species / memories forever....:-)