I grew up near a zoo that's pretty big and tends to take really good care of the animals. Some exhibits, especially those in the newer Africa section, don't even have any obvious fences because the cages were designed with natural walls. The result was that while they had some older exhibits that felt like jails, those were being phased out in favor of the more natural ones.
When I got older I was surprised to find out that exhibits like that weren't normal. It wasn't normal for the tigers to have 2-3 acres of land, with visitors viewing the tigers from bridges. It wasn't normal for the ostriches, elephants, zebras and giraffes to share a massive exhibit covering a quarter of the park.
What was normal, was putting them in tiny boxes.
What the fuck?
However, it is because of my experiences growing up that I believe zoos can be ethically created and maintained. The issue is that they need a lot of space and funding to do so, which they rarely get.