What role does fate play in the downfall of Macbeth?

I would prefer to read MACBETH more as a tragedy of character than as a tragedy of any dark fatality. Even if we like to assign the tragedy of Macbeth to Fate, that fatality lies in his character. The three witches may appear as the 'fate sisters', but Macbeth's 'vaulting ambition' which leads him to his downfall was already present deep in his mind. His immediate responses, especially his asides in act1 sc.3, suggest this evil seed in Macbeth. If we hold Lady Macbeth responsible for Macbeth's downfall, we should remember how Macbeth sends letter to his wife briefing her all about the witches and the good chance of their prophecy about his kingship come true. The conflict between his ambition and his conscience--the 'foul' and the 'fair' battling each other in him-- leads to a series of crimes, to his death in the hands of Macduff. Shakespeare dramatises the story of a moral-psychological conflict, a morality play to highlight the Renaissance contradictions in his protagonist.