"It's not your heart I want to break."

When it comes to untrustworthy feelings, there's always sadism. Anyone whose ethical system depends on people knowing (or even being able to figure out) what they want is going to run into the thorny problem of schadenfreude sooner or later; people, it must be said, want some pretty sick stuff, including public hangings and the scapegoating of sacrificial innocents. (Yes, I've been associating with a lot of utilitarians lately, why do you ask?) Or, as Eve put it, you can't base your morality on doing what some person ("Lisa," say) wants, because "Lisa can definitely surprise you—and, if you indulge her every will, she's likely to surprise you in some unpleasant ways!"

To get a better feeling for how natural sadism is, read this paragraph from a review of Cruel Delight: Enlightenment Culture and the Inhuman:

. . . the facts of cruelty—of the taking of pleasure in the spectacle of the suffering of humans and animals—presented a deep and ultimately insuperable problem for a naturalistic eighteenth-century ethic based on sympathy. Such an ethic had immense cultural power at this time, sustained by its imbrication with a dominant physiology and aesthetics of sensibility. But if not everyone is spontaneously moved to pity the dying lamb and the starving shepherd—if on the contrary there are those who delight in inflicting pain—then how can it be contended that a largely utilitarian morality of promoting pleasure and minimizing pain has a natural basis? Pity would have to be a universal response, or overridden only in specific circumstances, as for example when contemplating the punishment of a brutal murderer. Steintrager contends that a "solution" to this problem was to label those who delighted in cruelty as "inhuman." So pity was a human universal. But such a solution is in fact no solution at all: it is a trick, a tautology which dodges the issue.

Or you could stick with the Poulos nutshell of same:

Maybe sentimental ethics can't survive the death of humanism. But if humanism can survive the death of sentimental ethics, why does the conversation keep turning to de Sade?