One of the most frightening elements to Macbeth is what can happen when a moral order is not present to guide one's actions. The absence of this structure is when pride and ambition are allowed to run abounded. In this process, one can see how the continual appropriation of the world in accordance to one's own subjectivity can result in horrifying and morally bankrupt realities. Macbeth's own sense of pride in his sense of self and what is owed to him, according to his own calculations, allow him to succumb to the darker elements of his nature. It is pride that allows him to be persuaded by Lady Macbeth in believing that murder is an appropriate avenue to pursue in the fulfillment of his own ambition. I would say that the lack of a structure which would allow him to guide his actions in accordance to an unassailable good might be a reason why pride and ambition work on Macbeth to take the course that he does.
In my opinion, it is ambition rather than pride which is responsible for the undoing of such a brave and admired general as Macbeth. A secret ambition, exteriorised by the witches' prophecies and further enhanced by Lady Macbeth, (mis)guides Macbeth to the killing of king Duncan. At no point before the murder of Duncan, Macbeth displays any sign of pride. On the contrary, he betrays doubt, hesitation & moral scruples, his imaginative conscience holding him back from the murderous deed. Ambition for power, fears with regard to the means of attaining power, increasing fears as to how the power attained could be retained, the constant conflict between forces of 'fair' and those of 'foul', lead Macbeth on to the murders of Banquo and Fleance, of the family of Macduff, to his own death and destruction. At no stage of his career in Shakespeare's play, does he show pride in his evil and tyranny as a usurper king. Macbeth therefore shows the fatal dangers of 'vaulting ambition', rather than of pride.