that's valid, but it's a tradeoff too. living in the wild can be brutal. zoos bring empathy for animals to people who are otherwise shielded from the wild.
with that said, i'd be happy if zoos (and the pens within) were 10x-100x bigger.
How do you know that? Descartes believed that animals couldn't feel pain. We're all shocked by that now, but he could have (in fact probably did) use an argument similar to "that's anthropomorphising".
There's a long history of humans making claims about what animals don't experience, in order to justify how we treat them, only to later discover evidence that overturns the claims. It seems to me that this has to be the default explanation for zoos as well.
Not sure why you are asking this, but there's evidence that plants do feel pain.
At least some can emit chemicals to signal to others of their species that they are infested with harmful insects so other plants can begin producing toxins to protect themselves from infestation. Some also emit a pulse when damaged, which one might think if as kind of like a scream, though it's not anything humans can perceive with our innate senses.
(At least, not most of us. There may be exceptions. Some humans are abnormally good at sensing magnetic north, etc.)
A stimulus reaction isn't the same thing as "feeling pain", which requires a certain level of consciousness. It's debatable if even lobsters for example have the necessary development.
... And what if we are enjoying it? Could that mean there are animals that do, in fact, enjoy living in a zoo? Many animals at my local zoo are rescues, so perhaps living in confinement beats dying to those animals?
It doesn’t help now (at least not live, but you can watch highlights) but there are some webcams at Brooks Falls in Katmai, where bears famously congregate each summer to fish the salmon run. I watched quite a few good shots last June/July. Probably plenty of other webcams on that site I have yet to check out.
