David Hume famously argued that rationality had everything to do with formal consistency of our choices, and nothing to do with the content of our individual preferences; Hume thought motives and preferences were immune to choice and argument. In this view, there is no way you could rationally judge a preference:

'Tis not contrary to reason to prefer the destruction of the whole world to the scratching of my finger. 'Tis not contrary to reason for me to chuse my total ruin, to prevent the least uneasiness of an Indian or person wholly unknown to me. (Treatise of Human Nature, III.3).

This view has more or less become common currency among economists and rational choice theorists. But even they reject as mad some behaviors based on highly unusual preferences - what do you think, for example, of the man who fucked up his whole life for the pleasure of having a naked woman with rubber gloves clean up his house?

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