Zoos - Good or Bad?

I am absolutely fascinated by animals and a huge fan of them. I love to travel and see them in captivity. I also have seen what certain nature preserves have done to benefit endangered species. Certain zoos have also put forth effort in rescuing, breeding, and the conservation of certain species as well. Zoos are also nice for people who can't afford to go to Africa and go on a safari to see elephants, rhinos, and lions in real life.

Here's the problem, is this fair to the animals? Is it right? Is it like prison for animals and for our enjoyment mostly? I've also been to zoos in unregulated third world countries. I cried at the conditions they had those animals in there. Small cages, no area for shade, obvious signs of malnutrition, fur patches missing, etc. I think those places should be shut down. I hate that those places are put in the same category as reputable zoos across the world. Even on that note though, I feel like nice zoos need to make some of their habitats much larger. Not that this place is reputable, look at Sea World. That place is absolutely disgusting how they treat those animals.

I'm at a loss here. Are zoos good or bad? Do the benefits outweigh what's bad about them?