From what I understood from the article, they closed the exhibit because they didn't want the visitors to see the (potentially unsettling/traumatizing) injuries on the baboons. Which actually sounds reasonable to me.
Point being, eventually… A zoo probably does not want 4 year old children looking at a baboon with the side of its face torn away to expose the bone. In this case, "think of the children".
At some level, however, if I'm not comfortable cutting the throat of an animal that is staring at me in fear, how comfortable should I be eating meat?
Have they tried closing the Zoo and releasing the animals back into the wild. Zoos are a nineteenth century anachronism, designed for when that was the only way people could get a look at such exotic animals. Last time I was in one, the animals looked tired, stressed and listless.