First you have to accept the idea that each of us have free will. If that is the case then surely Macbeth too would have free will. Therefore, he could not blame his fate of the predictions of the three witches. Nor could he claim his wife "made him do it." At each step in the play Macbeth is confronted with his own conscience ("Is that a daggar I see before me?") You could argue that his increasing inability to sleep, his night terrors, hallucinations etc all are the result of his conscience bothering him. He becomes so deplete of rational thinking that by the final battle he resigns himself to his death at MacDuff's hands.