“I don’t think he’s mad, just devious in his sanity” inverts the usual moral logic. We excuse madness—the insane lack agency, can’t help themselves, deserve treatment not condemnation. But someone sane and devious chooses deliberately. Their clarity enables deception, exploitation, calculated harm. Sanity becomes the indictment.
This matches Arendt’s “banality of evil”—ordinary rationality enabling atrocity. Psychopathy research confirms: manipulation requires intact cognitive function. Understanding others well enough to exploit them. Maintaining false narratives. Passing sanity tests while pursuing destruction.
Sound reasoning doesn’t guarantee sound ethics. Sanity provides tools—self-control, planning, social understanding—that serve whatever values direct them. The devious sane person has the full instrument intact and aimed at corrupt purpose.
Sources:
- Walter M. Miller Jr., A Canticle for Leibowitz, 1959
- Hannah Arendt, Eichmann in Jerusalem: A Report on the Banality of Evil, 1963