While Lady Macbeth is certainly a factor in Macbeth deciding to kill King Duncan, she really does not bear the responsibility for his actions. After all, Macbeth has free will. He does not have to listen to Lady Macbeth; he makes a choice to listen to her. What causes Macbeth to go from innocent to striving to kill anyone who gets in his way is his overwhelming ambition. Macbeth is a tragic hero, and a tragic hero always has a tragic flaw; in other words, a part of his character that causes his downfall. In Macbeth’s case, he has the flaw, ambition, to begin with, but there has never been any reason for him to act upon it. When he meets the witches, they put the idea in his head that he can be king.
After Macbeth hears from the witches, he struggles with his conscience. He knows that Duncan is his kinsman, his king, and his guest. He knows he is risking his immortal soul. Yet, he still decides to kill the king in the end. Lady Macbeth may be calling him a coward, but he makes the choice to actually carry out the deed of killing the king. After Duncan’s death, Macbeth starts killing any person he thinks will get in the way. He kills the guards because he is afraid they will give him away. He kills Banquo because Banquo won’t give him the unquestioning allegiance he wants. He kills Duncan’s family because he is angry with Duncan.
All the deaths could have been avoided if Macbeth had not been ambitious in the first place. However, after he starts killing, he feels he has to continue or lose the crown for which he has sacrificed his immortal soul.