Macbeth's cruel deed is justified by his desire to hold on to his power. Macbeth sent these two men to murder Banquo and his child Fleance because they were standing in the way of being crowned. Macbeth's actions demonstrate that he will stop at nothing to become King, even if it means resorting to murder to achieve his end goal. .
Later, after Macbeth's confrontation with Banquo's ghost, when speaking to Lady Macbeth about the events that might follow for them, he states, "For now I am bent to know, by the worst means, the worst. For mine own good,All causes shall give way. I am in blood/stepped in so far that, should I wade no more/returning were as tedious as go o'er." (III, iv, 167-170) This quote reveals an awareness by Macbeth, of the magnitude of his crime "I am in blood", and an acknowledgement that he can not stop now, "should I wade no more". Macbeth's motivation in serving his own good, "For mine own good, All causes shall give way", allows him to reconcile the crime and move forward in the spirit of self-interest. In a subsequent scene, Macbeth confronts the witches in their cave, demanding them to answer his questions so he can know more about his future. He is persistent in his demand when he says, "Answer me.Though you untie the winds and let them fightAgainst the churches, though the yeasty wavesConfound and swallow navigation up, Though bladed corn be lodged and trees blown down" (IV, I, 51-64) Macbeth is determined to get the "answer" he wants from the witches and he will do anything to get these desired answers. For example, he states, "Though you untie the winds and let them fightAgainst the churches,though the yeasty wavesConfound and swallow navigation up" which shows that his obsessive desire for answers trumps even adverse events potentially threatening the good of Scotland. This reflects his blind ambition because when it comes to his prosperity, power, and his own future, nothing will stand in his way.
