Why does Macbeth slaughter Macduff's family?
Macduff harbors suspicions about the actual murderer of Duncan, is notably absent from Macbeth's coronation and joins Malcolm in gathering and leading the forces that defeat the play's title character. Learning that Macduff has turned against him, Macbeth dispatches murderers to kill Macduff's family. Apprised that this heinous act is at hand, Lady Macduff reacts by asking the messenger "Whither should I fly?/I have done no harm" (IV, ii., ll.73-74). Unlike the other evil deeds that Macbeth and his wife commit, the slaughter of Macduff's family has no instrumental value; it occurs after Macbeth has realized his ambition and does nothing to cover his crimes. That is, in fact, the point: Macbeth's evil is now so deep that it is without any human purpose. Lady Macduff is the only "human" female character in the play other than Lady Macbeth. By showing us Lady Macduff as a fond mother, Shakespeare heightens the contrast between a "natural" family and the unnatural character of the childless Lady Macbeth.