While Macbeth is, indeed, enticed by the predictions of the three sisters, his warrior-loyalty to King Duncan, as well as his blood kinship to the ruler, effect internal conflict. Thus, within Macbeth there is the conflict between what is "foul" and what is "fair" since the witches consider evil deeds fair and Macbeth's "vaulting ambition" interprets them likewise, his conscience yet recognizes the foulness of regicide and the evil of upsetting the Chain of Being, as well as the dangerous implications of having King Duncan die in his home.
These are the conflicting feelings and ideas expressed in Macbeth's soliloquy of Act I, Scene 7, in which he first wishes that the assassination can be done quickly and successfully:
If it were done quickly. If th'assassination
Could trammel up the consequence, and catch,
With its surcease, success; .... (1.7.2-4)
However, Macbeth also realizes that there are always consequences for actions,
But in these casesWe still have judgment here, (1.7.7-8)
Besides, this Duncan...hath beenSo clear in his great office, that his virtuesWill plead like angels, trumpet-tongued, againstThe deep damnation of his taking-off; (3.7.16-19)