Follow my logic, here. A zoo is a place that makes money out of exhibiting animals. If they DO NEED a certain animal for display and happen to get it from rescue (for free) that's great for them. So there should be a law saying they CAN'T turn another animal down when they don't feel like it. Such law would make sure zoos contributed with what is suposed to be one of their goals: the preservation and care of animals. And not just a money making place.
Love will take you far and hate even further.