Why So Sad?

I went to the San Francisco Zoo this past weekend with my BF. It was a really fun day, but I've decided that I don't think zoo's are ethical. Especially in this day and age when we know so much about other animals, it seems pretty ignorant to think they could ever be happy in the little enclosures zoo's are able to provide.
Especially for primates (and in marine parks I would include dolphins). I think that while certainly not exactly the same as humans, both primates (apes in particular) and dolphins have all the necessary faculties to experience boredom, sadness, hopelessness and probably something similar to depression. And for those reasons I think essentially having a gorilla enclosure, or a chimp enclosure is just as inhumane as capturing a bunch of people and forcing them to live in a trailer together.
Case in point, the silver back gorilla at the zoo the other day. At first he just sat there watching all the people taking pictures of him (myself included). But the longer we stood there the more apparent it was that he was actually watching us. He looked at each person, observed their expression, scowled when a baby started crying. It was weird, but I could tell he was thinking, AND I could read his facial expressions almost as well as I can read a humans. He was sad. And bored....and feeling trapped and helpless. I could actually see the frustration in his eyes! It was so awful, because I know that his situation wont be getting any better. His life is pretty much set, and the rest of it will be spent in that little fenced in patch of land.
After a while he went and sat in the doorway of his shelter, away from the people and the prying eyes. He just sat there, frowning, and sighing, shaking his head and rubbing his eyes and brow in exactly the same way I do when I am stuck at work and itching to get out of there. He was so unhappy. Even the little kids noticed and inquired of their parents why he was so sad.Ironically most of the parents couldn't see it. They said things like "He's not sad. That's just what gorillas look like."
The chimps were in no better situation. If anything their enclosure was worse. Not that the zoo people aren't trying, but what I mean is that compared to their natural habitat even the best enclosures fall woefully short. And this was not the best. The chimps seemed a little...crazy. I've read a great deal about them, and at least have a marginal grasp on their habits, and the chimps there were...off. Like they were patients in a mental hospital. One was zoned out, another grooming himself to the point of rubbing bald spots into his hair. They had a sedated/ bang-your-head-against-a-wall kind of vibe going on.
But the enclosures for many of the other animals were just as inadequate. The bears, lions, tigers, all had such small areas. They couldn't even get up to a full speed run in the space available to them. Again, I don't think zoo keepers are out to emotionally scar the animals, but...For as much as I enjoyed seeing them in real life it just felt...wrong.
To take a polar bear away from it's home on thousands of miles of moving ice, and put him in a 3,000 square foot enclosure just seems...terrible. To take a hippo who's natural habitat is the whole of the Nile River and put him in a corral with a tiny 10x15' pool of water (that he can barely turn around in) doesn't seem quite right.
For certain animals, like fish, insects, reptiles, most birds, rodents, and domesticated animals I think zoo's are a fine idea. A friend of mine mentioned a particularly content and jolly raccoon at a zoo he visited recently. And the goats at the SF zoo seemed pretty happy to be fed and brushed by patrons. Cool. But to take large animals, or smart ones and force them into tiny spaces for the rest of their lives is not humane. And I think the whole idea of "captivity" creates a division between us and them that really isn't there. We'd never put people in zoo's (although we do lock them in cells as punishment!) because it would be wrong, on so many levels that are obvious to everyone. So how is OK to put a chimp or gorilla in one? I think the answer is because most people don't see us and "them" as part of a continuum, but as two completely un-relateable things. And that is a mistake. We should know better than that.
And the truth is we don't need zoo's anymore to connect with the animal world. With all the beautiful documentaries out there, and 3d capabilities, we can virtually explore other animals and their awesomeness in their own world, where they belong. And they are more interesting to watch when they are in their native environments, doing what evolution has honed them to do.
I'm not sure what I'd suggest we do moving forward since all the animals currently in captivity probably don't have the skills to survive on their own. Maybe, as sad and unfair as it may be, the only thing to do is let them finish out their lives in the zoo, but stop replacing them with new animals once they are gone.
What do you think? Do you have any thoughts about this issue?