The basic challenge posed by Robin is this.  To support the imposition of a paternalistic government policy on Peter, one must believe that: (i) the government is sincerely motivated by Peter’s welfare; and (ii) the government knows what’s best Peter better than Peter himself does, even taking into account the fact that in the absence of paternalistic policy Peter need not rely only on his own knowledge, but is free to seek the uncoercive advice of anyone willing to give it to him, including the government itself.

To my mind, point (ii) is the easy part.  There really are people who left to their own devices will ingest poisinous miracle cures and the like, and who really would be better off if they didn’t do so, and for whom actually existing paternalistic policies are the only hope of being saved.  Of course there are some cases where the government really just doesn’t know better and gets it wrong.  Robin and I would agree that these are the cases where policy should be restrained, and if it’s not restrained it’s more likely to be an abuse of power issue than an ignorance issue.  So in my view the real action is in point (i), the extent to which the government will shun restraint and abuse or misuse the coervice power that paternalistic policies give it.

This is a problem; there are good reasons to be afraid of government power, which has been and continues to be hideously abused in large parts of the world.  In my debate with Robin I repeatedly argued that things are different in "well-functioning" societies like the United States, by which I meant that such societies are likely to have governments that, humanly and imperfectly, can both gather the necessary expertise and exercise the necessary restraint so as to successfully carry off a modest paternalism mission.  Robin correctly responded that the mere fact that we are a more or less well-functioning society does not prove that paternalistic policies are good; maybe we’d be in even better shape without those policies.  And as Bryan Caplan pointed out after the debate, not even the fact that there have been big reductions in the kinds of bad things that paternalistic policies are supposed to prevent (people getting poisined by food and drugs, people getting fleeced in pyramid schemes, poverty among the elderly, etc.) proves the point; those improvements might simply be due to the fact that we have gotten richer and better educated over time.

So why do I think that well-functioning liberal societies can get this stuff more or less right when I concede that most societies across space and time get it wrong?  The basic answer is that non-liberal societies get everything wrong.  In my view, the ascendence of the Enlightenment principles on which modern liberal socities are based is the most important thing ever to have happened in the history of the world.  There is an almost complete overlap between the set of countries that are based (in practice, not just on paper) on Enlightenment principles and the set of countries that are fit to be inhabited by normal human beings.  The empirical evidence of the success of the Enlightenment project in general couldn’t be more overwhelming.  So the fact that that there are other paternalisms out there that I would disapprove of no less than Robin does (say a religiously-based  controlling of Peter’s sexual behavior to save him from hellfire) doesn’t strike me as a strong argument for doubt about paternalistic policies that I might consider favoring.

This doesn’t solve the problem of "how can I be so sure I’m right that I can justify imposing my opinion by force," but it does give it different contours.  We should think about paternalistic policies the same way we think about other policies whose effectiveness we can’t be completely sure of.  We don’t look for guidance to all the many failed societies.  We use some combination of reason and evidence, including reason and evidence about potential abuses of government power, and we do the best we can.  And we have made progress.  We know more than we did in the past about the kinds of things that lead people to self-destrictive behavior, and we are reasonably good at parcelling out government power so that it doesn’t get abused too much.  This is new, and it makes all the difference in the world.  The fact that we are not perfect at it is both an argument for restraint and an argument for trying to get better at it.  If the Enlightenment project progresses even more, I’d probably favor even more paternalism.