While I LOVE this concept, I see alot of people campaigning to close zoos, when it's not that simple. Present day accredited zoos aren't just going and capturing animals out of the wild just to place them in captivity & put them on display. https://twitter.com/LoveAndShalom/status/1287150038188253186
Many zoo animals are rescues. They were once kept as exotic pets, kept in bad conditions at for-profit wildlife parks, came from "bad zoos," etc. After they've been in captivity for so long, you're going to encounter a whole lot of issues attempting to release them into the wild.
It's not as simple or black & white as "letting them go." Unfortunately, the reality is, many early zoos DID go and capture animals from the wild, for the sole purpose of putting them on display. But alot of that cannot be undone after years of generational captivity.
Also, credible zoos are doing wonders for conservation efforts. Sometimes, animals can be released back into the wild, & these conservation efforts help with declining populations. But also, some species unfortunately end up severely endangered or extinct no matter what :/
There's some species that you can only find in captivity because they've gone extinct in the wild. Not because of them existing in zoos, but due to other reasons (poaching, habitat destruction, etc).
And most of us generally agree that we'd rather see these species alive (while properly being taken care of) in captivity than lost forever, especially if there's a chance that if breeding programs are successful, a wild population can potentially be re-established in the future.
Always be critical of how we take care of wildlife in captivity! But unfortunately, captivity isn't always black & white, & is not only sometimes necessary, but also beneficial in saving species that are on the brink.