@ThylacineAlive You raise an interesting point concerning the viability of populations of rare animals. Maybe of the rare animals in zoos. Especially if they are rare within the zoo community, don't have viable populations if we look 20 or more years ahead. I recently saw a presentation at Burgers Zoo about breeding and viability of populations within zoos of certain species, it doesn't look good. For many populations the number of animals and genetic variation is simple to low for future sustainable population holding. I believe that something like 75% of bird species and 30% of mammal species, don't score viable for self-sustaining populations at the moment.
Now one can question what to do with populations that don't seem viable in the long run. In Leipzigscase some animals certainly are within this category. Where even the best conservations efforts probably won't deliver us sustainable populations in zoos, let alone reintroducing them for the wild. As it currently stands. Although I do still love to see them and think they could be great ambassadors for their last wild cousins. Personally, I don't know to evaluate this dilemma.
I don't like or think it is ethical to bring wild animals into captivity, even though it could certainly help with the genetics problem. The only for reserve population purposes this might be done if you ask me. Like with the Tasmanian devil.
To conclude I think we should celebrate the rareties we currently have in zoos because in 20 years most animal species in zoos will be relatively common.