My apologizes David, regarding shows in zoos, I was generalizing about any animal show in a zoo. Looking back at my posting I failed to mention that specifically.
Should we regard elephants with thoughtful activism without showing respect to other animals?
My general experience with animals shows in AZA zoos is that they are excellent vehicles for entertaining conservation education. The San Diego Zoo has an excellent sea lion show (where I believe the sea lions are non-releasable rescue animals) and the LA Zoo has an excellent bird show. The animals perform natural behavior based "tricks", but there is an underlying conservation and/or natural history lesson to them. If circuses found a way to do this then perhaps there would be less of a stigma against them at least in the zoo/conservation community, but it doesn't seem likely that will happen (but would be very interested to know if it is going on anywhere).