How far fate is responsible for Macbeth's doom?
That depends on how you view free will v. fate. Was it fate that Macbeth should run into the witches on the heath in Act 1, sc. 3 or were these witches somehow already aware of Macbeth's character and secret desires, so they just took advantage of his character flaw? An argument could even be made that it was possible one or more of the witches had overheard, somehow, that Macbeth was going to be named the new Thane of Cawdor, so even planting that seed of belief in him may have been contrived. Certainly, even though the witches correctly named Macbeth the Thane of Cawdor, Macbeth still had free will to do what he wanted with the information or to ignore it completely. Macbeth did not have to kill Duncan; his wife talked him into it. Would she have been able to if he hadn't already thought of it himself and if he had been of stronger moral character? Probably not. Macbeth did not have to hire killers to kill Banquo; he did that out of paranoia and a frustration at the future prediction the witches had made of Banquo and his descendants. The witches again meet with Macbeth later in the play (Act 4, sc. 1) and tell him to beware of Macduff. This makes him even more suspicious of Macduff and he then decides to have Macduff's family killed. Again, he chose to do it. Even when Macbeth meets Macduff in Act 5, sc. 8 and Macduff kills Macbeth, choice was still the factor. Macbeth could have fled the castle when things started disintegrating, he could have avoided the duel with Macduff, but he instead stays and meets Macduff head-on (sorry, couldn't resist the pun). Macbeth made his decisions based on his personality; he was ambitious and ruthless. His moral fiber was weak and he was self-centered. He could blame fate, but it would be another sign of the weak, irresponsible character he was in the play.
I would like to read Macbeth as essentially a Renaissance play dealing with the tragedy of 'vaulting ambition' in a fast-expanding world, in a world in which individual will locked its horns with dark fatality.
If we tend to conclude that Macbeth shows fatal victimhood, it is surely an unjust negation of the worthiness of 'Bellona's bridegroom', of the story of the fall of the brightest of angels in the muddled heaven of Scotland. The fact that Macbeth was an incomparable soldier, a great saviour of Duncan's Scotland, should not be set aside in a bid to prove his victimisation in the hand of Fate, the witches serving as agents of inscrutable fatality.
The story of Macbeth is one of temptation and fall. But did the witches tempt Macbeth? Surely not. The witches' proclamations were but an exteriorisation of the seed of evil already in Macbeth. Macbeth is an example of a self-divided personality, the unlawfully ambitious Macbeth tempting the Macbeth of imaginative conscience and moral scruples. Shakespeare dramatises the theatre in the soul of his protagonist through soliloquies and asides.
'Macbeth' is a Renaissance Morality play, a play that reveals the battle between predestination and free will. Macbeth's fall is chiefly due to his submission to the temptation within himself, rather than any hostile predestination. The witches led a trap; Lady Macbeth stood actively by him; but, after all, it was his own ambition which paved 'the primrose way to everlasting bonfire'.