On the one hand, zoos do valuable research/conservation work and educate us. On the other hand, the animals are enclosed in a small unnatural environment and lack stimulation.
I think it's a bit of a grey area. One of my happiest childhood memories is the day my mum had a job for the day in Bristol, near the zoo. My dad dropped her off at work and then we went to the zoo ALL DAY. We were the first people in and the last people out. And my dad bought me a badge with a tiger on it.