When I was a kid, I loved going to the zoo. I loved the reptile exhibit the best, but also the lions, parrots, gorillas, elephants, and basically everything. They were some of my best memories.
But as I got older, I began viewing most of the stuff I once liked as ethically problematic, including zoos. There are some zoos that seem to give the animals enough space to move, but they still can't fully simulate their natural environment with hunting and such. But they're probably more physically comfortable with longer lives, no threat of starvation, access to veterinary care, etc. Like a human in a cubical farm, basically- comfortable but not exactly right.
Humans don't build zoos for the animals; they build them for humans. That alone almost says enough. When humans want to do things purely for animals, they build conservation parks, where they basically just fence off, protect, and monitor a natural piece of the land. Lions hunt antelopes, the cruel cycle of predator and prey continues, and they're all happy, except for the prey.