I'm not saying that all circuses are like this, so please don't misquote me on this, but a great majority of them are. Besides, at least zoos tend to have enclosures for their animals. How would you like to be in a cage, basically it's like being sent to jail for animals that are supposed to run wild and free.
And not to mention the fact that wild animals have been killed simply because they are acting out of pure instinct when it comes to attacking humans, but instead of blaming man's stupidity, guess who winds up getting shot for it in the end? Don't get me wrong, I am not some PETA nutcase, I just wish that people would learn to open their eyes on the real issue here.