I believe that the problem with modern zoos (and by that I'm also talking about Aquariums, Safari Parks, etc.), those that work for animal conservation, is that while they have evolved, the common people have not, still seeing zoos as a mere spectacle. And while the conciousness of animal welfare has risen in the general population, their knowledge and empathy are still extremely low. A huge threat to zoos is "Animal Rights Defenders" who hound down modern, scientific zoos with bad press, while forcing their cats and dogs into veganism (THAT is animal abuse!). If it were a vocal minority, that wouldn't be a problem, but they easily contaminate social networks and, therefore, popular consciousness. Many times I've seen zoo patrons banging at the glass to make an animal move and, should that fail, they acccuse the zoo of boring and drugging them, and leave nasty reviews on Google Maps.
My dear Barcelona Zoo has been pretty much destroyed in the public eye thanks to viral rumors and lies that people believe due to their lack of knowledge and their tendency to regard anything horrible as true. It's come to the point that there's an imminent threat that these liars, who have political connections, could close down the zoo. The current mayor, for example, cut the funding for the new dolphin lagoon plan, and insists on the dolphins being moved out, not an objectively bad idea, but it takes away from a plan that could have actually worked. She criticizes the captivity of dolphins of being a mere spectacle, even though Barcelona Zoo has cancelled yhe shows for about a year, and the dolphins are being moved to Valencia, where they do shows! Makes a lot of sense to me! For zoos to "clean their name" in the public eye, the public eye should stop looking at gossip magazines, sports and online mendacity, and instead take more interest and actually LEARN about animals, what they are and what they need.
Also, on a different note, I believe that many smaller zoos, such as urban collections, will have to optimize their space. London Zoo is a good example of this practice, and I believe that places like Barcelona Zoo would benefit from having less animals and more space for each.
I hope my two cents don't feel like two tons.