In light of the German cannibalism case, Will Baude ponders the public policy implications of irrational preferences, such as the desire to be killed and eaten. Will writes:

Anyway, my own inclination is to say that it’s a bad idea to pretend that such people held preferences other than the ones they actually do have, a bad idea, therefore, to keep them from harming themselves if that’s what they want to do. Even if the preference is irrational, it’s still a preference.

This is probably a topic way to big to be treated effectively in one blog post. I’m sure philosophers have written entire books on the topic. But let me throw out a suggestion. One key to determining whether a preference is irrational, and hence whether there is a legitimate paternalistic interest in suppressing the fullfillment of that preference through public policy, is whether those who have that preference also have a second-order preference not to have that preference. (This is neither a necessary or sufficient condition. At best, it is one disjunct of a sufficient condition.) We can no longer ask the poor, err, victim in the German cannibalism case whether he would prefer not to have a death wish, but he well might have said yes. Similarly, it seems to me from talking to smokers, that many of them not desire to smoke, but they would prefer not to have that desire: hence their usually futile attempts to quit.

It seems to me there are three sorts of reasons that one might have a second-order preference not to have have a given preference.

1. A person might prefer not to have a desire because she knows the desire will go unfulfilled, and this lack of fulfillment causes mental anguish. One might desire to have sex with some movie star, but knowing this lust is certain to be unrequited, one would prefer not to have this desire. I don’t see much scope for paternalistic public policy in solving the problems created by these sorts of desires. And I wouldn’t call these desires irrational.
   
2. A person might prefer not to have a desire merely because of public policy itself, whether formally written into law or as part of informal societal mores. A gay man might prefer not to have the desire to have sex with other men, not because of anything inherently bad about gay sex, but because of the potential for being arrested (pre-Lawrence), or because of widespread bigotry against gays. In this case, public policy is the problem, and so there is no excuse for paternalism. Nor would I call these desires irrational.
   
3. A person might prefer not to have a desire because the desired entity is intrisically bad, i.e. it conflicts with other more strongly held prefernces, out of physical necessity. The German cannibalism victim might have desired to have a comfortable retirement sailing about the Mediterranean, but he could not fulfill both this desire and his desire to be killed and eaten. Many smokers wish to have a long life, but their desire to smoke is in conflict with this. It is in this category that we find the truly irrational desires.
   

Only when the unwanted desires are of the third type is there a prima facie case to be made for paternalistic public policy. In the third case, the public policy might actually be helping the weak-willed person fulfill their second order desire, thus resulting in greater utility (if we define utility in terms of satisfied preferences, or use satisfied preferences as a proxy for utility).