The real dispute between the two Orders lay in the epistemology of inference; the nature nurture controversy, and religious disagreement. One relied on intuition, placed its faith in the power of heredity supported by training; the other relied on reason, placing its faith in the power of training aided by heredity. The BG tempered in the fire of the Butlerian Jihad-believed most fanatically "Thou shall not make a machine m the likeness of a human mind" and the other dedicated itself to making human minds in the likeness of machines. Though centuries of mutual mistrust neither benefited from the accumulated wisdom of the other.
Never attacking its methods openly, the Bene Gesserit secretly spread the word that Mentats could be undermined by self doubt. Openly the Bene Gesserit charged that Mentats could not adequately interpret the quality of the data they used. The Sisterhood read the language of the body in the nuance of a blink, a gesture a shrug and contrasted their additional channel of information with the Mentat reliance on discursive symbolic systems. The BG maintained that no Mentat could ever provide a full reading and thus could never offer complete advice.
Many lent some credence to the charge but discounted its importance to a Mentat's function.