What if your "Contract" as Lucian calls it, to join the Skyrim chapter of the Dark Brotherhood is to kill a pregnant woman marked for death like Rufio was? say she's marked for death for carrying the child of a count or a guard captain?
This would destroy the way people look at the Brotherhood now, as just a sort of club for assassins, and would instead show them for what they truely are; A Deranged Cult of Psychopaths and Serial Killers.
At the same time, it would also bring much, MUCH starker and more realistic reality to the game. And something tells me that the Dark Brotherhood wouldn't have nearly as many willing participants.