What it means to learn from history is not to simply admit things went wrong and assume you can do better. What it means is that understanding the causes and motivations behind a large-scale tragedy is key to prevent it from happening again. The Ascians are not a cause, they're an organization. Organizations have objectives, and we already know theirs is not genocide for genocide's sake. Obviously we can't let them kill everyone, but until we understand why killing everyone furthers their objectives, we can't really move towards conflict resolution. We can't even be sure that simply "defeating them once and for all" will actually change anything. And we're supposed to be better than that.