Something can be good and bad at the same time, life is complicated. A good zoo can really provide a good life for most, if not all, of their animals, as long as the keepers are well educated and have the resources to do so. In fact the lifespan of animals in a zoo can often far exceed the ones in the wild, as they tend to have fewer diseases, fewer accidents, actual healthcare, and aren't constantly trying to avoid getting eaten.

A good zoo also participates in research and breeding programs to keep the wild populations healthy.

That being said, not all zoos know, or care, how to keep their animals mentally healthy. Especially zoos that are really just glorified theme parks. There are definitely animals that aren't kept well, are kept in much too small of an enclosure, and have nothing to keep them busy.