Macbeth has many character flaws, but the one that is his downfall is his moral decline. As they say, power begets power, and Macbeth is an example of this. He convinces himself that he is the rightful heir to the throne, even though he has to kill the King to be so. At the start of the play, Macbeth is a hero, but he is easily swayed, shamed by his wife, he continues his downfall. His morals become less important to him, and power more important. Macbeth becomes evil because once he slips down that slope he slides all the way down and cannot claw his way back up to moral again.
macbeth character has many flaws. however it is the angle at which we approach his personality that one can accurately examine them. firstly, to look at it for the perspective of 'good' we realise that his morals have been severely compromised by the witches prophecies and the encouragement and intimidation by his wife, lady macbth which intensify his own ambitions. as the play progresses we realise that macbeth no longer needs the persuasion of these evil elements to conduct his evil deeds. this was shown when, without the knowledge of lady macbeth or any persuasion by the witches he hired three murderers to kill banquo and his son fleance.
Alternately, to view his personality from the 'evil' angle, we see that he is a week "villian" and still relies on the witches' prophesies to reassure him that he will not be beaten.