No worries!
I don't think many people realise the scope of work now that goes on inside a decent zoo. Most zoos don't breed for release into the wild any more - dangers of disease transmission etc make it an unfavourable option, but there are so many other ways they can contribute, and should be contributing. Not all do, obviously, and they need to start.
If you go to a zoo and see a cute animal that isn't endangered, it's there to pay for another, probably less cute, animal that is. The otters at Durrell, for example, through an adoption scheme, generated something like 4 times the amount of money they cost to keep. That money can then go back into funding work to try and understand a fungal disease that is wiping out frogs and toads across the world - but which doesn't 'sell' as well as a cute otter. Because of the otter playing in her pool at Durrell, the mountain chicken (a huge brown frog) has a chance at a future. Very few people donate direct to it's conservation though - it's not attractive enough - and no-one would pay to come and see it on it's own at the zoo.
As long as you stick to those animals which don't suffer especially by being in a zoo (like meerkats), I don't have a problem with this. I do have a problem with cetaceans, for example, and think you would have to put forward an extremely compelling case to justify keeping them in captivity.
I also think, once there, you are duty bound to provide the animal, any animal, with a good life. That includes an area which allows them to carry out natural behaviour (water for swimming, sand for digging, branches for climbing etc), some measure of privacy if they need it, and a range of interesting ways to 'find' their food - so at Durrell, a lot of time is spent hiding food either in the enclosures or in 'toys' or devices that can be thrown in for the animals to explore and shred! And shows, demonstrating unnatural behaviours, should be off limits. (Those that take the chance to show something the animal does naturally, I think, need to be discussed further).
The problem is that much of this work is either behind the scenes or taking place in another country, so it is easy to assume that all that goes on is people gawping at cute animals.