It's one thing to kill an animal in front of children and then throw it to lions. It's another thing to not do in front of children.
What do you think happens in the wild? Are you going to be mad at the lions who kill a zebra?
Exotic animals under a zoo's care are expected to be cared for, not butchered. A wild giraffe or zebra has the option to fight or run away from predators. They can bite/kick/ram into, or otherwise injure a predator. They also have the free space to be able to make an attempt to flee.
In a captive environment they don't have that option. It's not fair and the odds are 100% against them if humans have them captive and kill them.
At least if this was meat from a slaughterhouse it would be from animals that were intended for consumption. An exotic animal like a giraffe is an animal that the public should reasonably expect should be maintained for its natural life (as long as it's not suffering with a painful disease or incurable injury).