I'm just worried that as the barrier between humans and animals gets larger and larger people are going to stop caring about them. It's pretty easy for most people to brush off the destruction of precious habitat, accept pollution, and turn a blind eye towards poaching if they don't ever have a chance to see the animals in person. We as humans have a hard time understanding the suffering of large quantities of humans and animals in an circumstance, but when it's boiled down to a handful of stories or faces than it becomes understandable and emotional. Sea World gives a face to Orcas everywhere. When someones making a decision about whether to allow construction of something that could disrupt local orca populations they may not care, but if they can visualize the Orca they spent time with at Sea World it could influence their decision.
One of Zoos primary mission is to benefit the earth and help protect habitats from destruction at the cost of the animals freedom. It is an ethical dilemma because by putting my family with a couple feet of giraffe I'll never think of them the same way. They're real. Not just an image on a computer, but a real thing. I don't want that animal species to die, and I'll fight for their preservation. That's what Zoos do, bring knowledge and educate people through contact.
All that I've written above answers this, and I'll also add that you seem to be missing the fundamental connection people make at Zoos.
I'll leave it at this, but I still think this is way more multi layered than you think. I understand that if you, after weighing the costs, have decided no captivity is acceptable than alright. However, ignoring the benefits completely is not the right call either.