In his Pulitzer Prize-winning book, The Denial of Death, Ernest Becker (1973) suggests that we have it all wrong about who is and who is not mentally ill. Put more succinctly, our ‘pretense of sanity’ (p. 30) is a denial of our true condition. Centuries earlier, Pascal (1670/1941: 441) had a similar insight: ‘Men are so necessarily mad, that not to be mad would amount to another form of madness.’ We will delve into the logic of such aphorisms in greater detail in the pages to come but these, presumably, counterintuitive assertions have much to do with what I hope to explore in at least summary fashion in this chapter. First, I want to underscore, when all is said and done (organic disorders and sadistic serial killers notwithstanding), the elastic character of what is termed mental illness. Remembering Nils Christie (2004), insanity, similar to crime, is like a sponge that can absorb virtually any sort of behaviour as long as those with the power to define and the power to punish deem the appellation an appropriate one. The allusion to punishment and cognitive impairment, by the way, was hardly coincidental. The overwhelming number of US citizens diagnosed as mentally ill are housed in the nation's jails and prisons (James and Glaze, 2006). It is thus necessary to explore next why those determined to be mentally ill are almost inevitably incarcerated rather than consigned to a treatment centre. That will set the table for the exposition from psychological, criminological and theological sources that will seek to provide some logical coherence to this rather ‘bizarre’ practice of punishing those who, at least putatively, have diminished mental capacity. I will argue that the short answer to the conundrum, as contained in the title of this chapter, is that there is something in both their physical presence and in the message their eccentricity conveys that is deeply disturbing to the world of economic and political privilege and to the norms of what Foucault (1972) calls ‘true discourse’, or what otherwise might be termed ‘common sense’. That something is the prophetic; and, as with the classic prophets of ancient Judaism and their more modern counterparts, theirs is a scathing social critique, not to mention an ominous forecast, to which, as history repeatedly proves, few but the wise pay heed.