For me, it's always a case by case basis when it comes to things like zoos and animal preserves. In certain cases, there is plenty of space for the animal to graze and be happy and they have replicated a reasonable facsimile of the animal's natural habitat, which in some cases, may have shrunk or been eradicated all together, so the animal preserve/zoo may be the only place to save an animal from extinction.
However, from all the research we know about killer whale orcas, and one can even ignore the documentary if you like, due to it's inaccuracies (which are negligible in my opinion but if the biases there bother you, you can get your information all over web from other sources), orcas just do not thrive in captivity at all. It is a very poor quality of life for them, and the conditions, such as rewarding their tricks with feeding, such as one does with dogs, has proven to be disastrous to their behavior and temperaments. (Orcas who turn on each other and viciously bite the newbie orcas who are struggling to learn the tricks, thus delaying the feeding for all) Orcas are just too intelligent and proud creatures to endure being given the "circus" treatment. Captivity does to them what pitbull and **** fights does to those animals, unfortunately. There has never been an orca attack in the wild, only in captivity.
Also, orcas mate for life and maintain their family unit for life as well. Seaworld has been deliberately deceptive about claims they preserve the family unit - they do an initial overture of keeping them somewhat together at first, but the family unit is soon separated.
Then there is the issue of the dorsal fin collapsing from captivity. This doesn't happen in the wild either.
While the orcas in captivity now cannot be safely returned to the wild and survive, there are things such as "sea pens" which would be a great alternative. It would be the equivalent of what we call "animal preserves" for land animals. The orcas would swim in a large, closed off ocean preserve but would still be cared for by humans. Seaworld has the money, if it wanted to, to do the right thing and make these sea pens available for their captive orcas and give them a semblance of a happy life, but of course it would mean the end to their orca "program" of tricks for $$$.