You'll need to be committed to the cause of conservation, and believe that the wildlife of the world needs lifeboats. You may hate zoos per se. You may love them. You just need to be a constructive guide and critic. Think of theatre criticism, of film criticism.
Zoos are no different.
Visiting zoos needs to be uplifting and rewarding. We need to be enthused and educated. Many zoos simply depress us and confuse us. So next time you visit a zoo, take a notebook. Do some research.