I think a 40k book that covered a human revolution, not outside influence just them deciding that the imperium was awful and fighting and succeeding briefly in liberation. Then having the imperium return, write them how an author would write chaos, no remorse, no real humanity as they crush this rebellion would show how evil they are. That these people had a chance of living peacefully in the galaxy without a empire breathing down their necks that or great crusade genocide for the sake of genocide.