Here again were stand on uncertain ground. Almost certainly the Harpe family was Tories during the Revolution. Their father evidently fought for the British at King's Mountain, one of the decisive battles of the Revolution. The brothers' Tory sympathies are born out by Micajah Harpe's words to Lambuth, an itinerant preacher and one of few persons to survive a woodland meeting with the pair. After the brothers had robbed him, Micajah Harpe opened Lambuth's Bible and saw the name of George Washington written there. He is supposed to have said, "That was a brave and good man, but a mighty rebel against the king." Thereupon Micajah Harpe handed back to Lambuth the Bible and money. As the two rode off, they called after him, "We're the Harpes!" Quite clearly, even though Micjach Harpe admired Washington, his sympathies were with the king. Indeed very likely bitterness caused by the Revolution actuated the Harpes to enact a wild vengeance.
But this motive is unlikely to be the sole one. The Harpes were said to believe that they had been predestined by God from the beginning of time to commit murders. Indeed some sort of fascination with religion--perhaps even a mania--seems to have possessed at least Micjah Harpe, as evidenced by his sparing Lambuth. Later the Harpes disguised themselves as ministers and sought sanctuary at site of a recent revival. But again a religiously-oriented psychosis seems to be unlikely to be the sole cause of their rampage.
Very likely Micajah Harpe was paranoid and suffered some psychotic delusions. His legal wife, Susan, testified that because of his guilt, he at times was convinced that the ground was shaking. Wiley also might have been paranoid, but he also could have been psychopathic.
One aspect is very clear. The murders were not sexual. No evidence exists that any of the victims were sexually assaulted, nor is there a hint that the brothers' gained sexual release from their acts of mayhem. However, the mutilations of some bodies suggest that the pair were actuated by a wild, indiscriminate hatred of humanity. Indeed they seem to have been arch misanthropes. Perhaps the following statement of J. M. Beazeale, an early historian, though melodramatic to modern ears, captures the essence of the Harpes' behavior. He observes that they killed "not for spoil or plunder, but for the gratification of a hellish thirst for carnage, and a fiendish delight in human misery, that none could possess, but a devil incarnate, carrying within his unnatural and accursed bosom, all the rankling and burning furies of the infernal regions."
One can speculate as to the reasons for their savage rampage, but all one can really do is guess. Very likely more than one of these suggested motives were at works behind the murders, but to what extent this is true is difficult to assess.