Macbeth was a brave and fierce soldier, but that in itself did not necessarily make him a good man. However, he was also a man of conscience who believed in God's judgment. The idea of killing Duncan horrified him completely. If it had not been for his tragic flaw, ambition, the thought of it never would have occurred to him. Once his ambition had been aroused by the witches' prophecies and the idea of Duncan's murder had become a reality, Macbeth agonized over it and struggled against the evil of it. He told Lady Macbeth that they would not proceed. His decision was a moral one, but he did not hold firm to it when Lady Macbeth questioned his strength and masculinity and reminded him of his ambition, that Scotland's throne was within his reach.
When he actually murdered Duncan, he was sickened by what he had done; if there had been no inherent goodness in Macbeth, murdering Duncan would not have affected him so profoundly. Macbeth had, after all, killed many men before; the sight of blood was nothing new to him.
There are definite contradictions in Macbeth's character, though. He ordered the murders of Banquo, Fleance (who escapes), and Macduff's entire household, but at the play's conclusion, he did not want to harm Macduff:
Of all men else I have avoided thee.
But get thee back! My soul is too much charged
With blood of thine already.
Even after all the terrible deeds he had committed, Macbeth's conscience still spoke to him in the play's conclusion.
What we gather from the bleeding sergeant in act1 sc.2, Macbeth is a noble general, an exemplary soldier, 'Bellona's bridegroom', fighting for his king & saving Scotland from rebellion within as well as from military aggression without. But his noble heroism in war is no certain proof of his goodness, for the Witches spell out the paradox in their sinister chiasmus in the opening scene: 'Fair is foul, and foul is fair'.
Macbeth is both good and bad, fair and foul. He has the imagination of a poet & the moral conscience of a good man. But he also nurtures an evil ambition to be the king, a 'vaulting ambition' which is enhanced and enkindled by the Witches. In act1 sc.3, after prolonged dwindling between the fairness and foulness of the 'supernatural soliciting', Macbeth seems to leave it to chance:'If chance will have me king, why,/chance may crown me'. When king Duncan and his men reach Inverness, Macbeth is too unsettled to receive the king as per protocol. In act1 sc.7, Macbeth reveals his divided self in his long soliloquy--'If it were done when 'tis done.....' He knows that murder of Duncan would be a breach of 'double trust' and such a crime would invariably invite punishment for the killer in this life itself. Subsequently, Macbeth tells his wife, 'We will proceed no further in this business'. Returning from Duncan's bed-chamber after the murder, Macbeth feels terrified to see his bloody hands. His sense of guilt and fear, born of his imaginative conscience, seem to have appalled him:'What hands are here? ha! they pluck out mine eyes!/Will all great Neptune's ocean wash this blood/Clean from my hand?'
Macbeth is not all good. No all good character is fit for tragedy. Macbeth's evil ambition, getting the better of his moral conscience, goads him to tragic suffering and eventual death. His hallucination of the air-drawn dagger just before the murder, his hallucination of Banquo's ghost in the Banquet scene, his observations on life on receiving the news of Lady Macbeth's death etc. suggest very strongly that there is a fair Macbeth underlying the foul acts of an usurper king.