How can Macbeth be interpreted as a victim of his time who was misled and manipulated into committing murder?
In eleventh-century Scotland, most people would certainly have believed in witches as well as a witch's ability, in part, to prophesy the future. Therefore, when Macbeth is confronted by the Weird Sisters, it is not a leap to assume that he will believe in their legitimacy. This belief would make him much more likely interpret their words as truth rather than to be on his guard about their motives. The audience gets clues about their motives, though, because we see them planning his deception. In Act 1, Scene 1, they discuss their forthcoming meeting with Macbeth, saying that "Fair is foul, and foul is fair" (1.1.12-13). In other words, things that seem good are actually going to be bad, and things that seem bad will truly be good. Thus, when the sisters tell Macbeth that he will be king, it will seem great though it will actually be quite bad. Hecate's later plan to "draw him on to his confusion" by making Macbeth feel "secur[e]" so that he lets down his guard and is rendered more vulnerable is further evidence that the Weird Sisters seek to manipulate Macbeth with their statements, and these statements will appear to be prophecy but are really designed to prompt Macbeth to behave badly in order to make them come true (3.5.29, 32). In this way, it is not fate that Macbeth kills Duncan, but it is rather the result of his being manipulated into corrupt behavior by the Weird Sisters, who he perhaps only trusts because such things are thought to be possible in his era.
Macbeth is manipulated by his wife and her arguments regarding right behavior for men in this era as well. In Act 1, Scene 7, he lists the myriad reasons he has not to kill Duncan, and the only reason he has to go forward with the murder is his "Vaulting ambition" (1.7.27). Moments later, however, he tells Lady Macbeth that he "will proceed no further in this business" (1.7.34). In other words, he has decided that ambition is not enough reason to commit this terrible crime. Lady Macbeth then attacks his manhood, saying that if he does not go through with their plan, he will have to "live a coward in [his] own esteem" (1.7.47). She implies that he is not a man if he does not act as they've planned, and she swears that she would kill her own child if she had promised him to do so rather than go back on a promise she made to him. In this era, men were very much supposed to be the kings of their own castles and masters of their families. By insulting his masculinity, or lack thereof, she suggests that he is not a man to be respected by their era's standards: for them, men should be ruthless, powerful, determined. For Macbeth to make a decision and then renege on it makes him seem weak, she says, and she is embarrassed by his weakness. Were the gender roles of this era less rigid, less polarized, then Macbeth might not have been so easily manipulated by his wife. In the end, his ambition is not enough to prompt the murder, but his pride is.