This thread contains SPOILERS from here on out. Read at your own discretion.
If you look at the targets that initiate you into the Dark Brotherhood on Oblivion and Skyrim....
The oblivion target was a man who had no more will to live. He just layed in bed waiting for death to come. You put him out of his misery.
In Skyrim, the child asks you to kill Grelod the kind. Spending five minutes in her presence could easily tell you why he left and wants her dead. She is making the lives of innocent children miserable, and she refuses to let them leave and be happy. Would it not be best to just...take her out of the situation?
What do you think about the morality of the Dark Brotherhood?