Animals should not be kept in zoos
On the one hand, the zoo animals are usually dangerous, then it is safe to keep animals in cages.
Wild animals can not be released when there are humans around because it is dangerous. The zoo would not exist if the animals could not be kept in cages, because they could not e fed or trained.
On the other side, some zoo animals are not well cared for. Animals must be free and not kept in cages, because it is their nature to live freely in the wild.
Normally the zoo animals suffer abuse, they are hungry. they are forced to live in cages until they die.
The animals that are kept in cages die before, they are not happy either
To sum up, I think the zoo animals must be cared for and fed correctly. If the animals are kept in cages, the cages have to be good to live.
It would be better not to keep animals in cages, but that's impossible.