I always thought the point of reading about historical horrors was to remind us of what happens when we stop paying attention, or when we start letting too many little things just pass without correction. I hope that reading about things like that makes the kids think, "How can people have let that happen?" and "What can I do to prevent it from happening now?" I hope that it makes them notice the little racist/sexist/oppressive things that might be happening around them now, and encourages them to put a stop to it before it becomes endemic.