Passage
The proposition that the state has no business criminalising conduct that harms no one but the actor wears the borrowed authority of John Stuart Mill, and the borrowing is not always honest. Mill's harm principle was offered as one limit among several on the legitimate use of coercive power, hedged about with qualifications that the modern slogan tends to discard. The slogan presents the principle as a clean line: conduct that affects only the actor lies beyond the reach of the criminal law, full stop. The difficulty is not that the line is wrong but that it is almost never clean, and the work of an honest criminal law is done not at the line itself but in the contested territory on either side of it.
Joel Feinberg's exhaustive treatment of the principle is the natural starting point. Feinberg accepted the harm principle as a genuine constraint but observed that 'harm to others' is a category whose edges are anything but self-defining. A great deal of conduct that looks self-regarding turns out, on inspection, to impose costs on others: the motorcyclist who declines a helmet consumes public medical resources when injured; the addict whose dependence is treated as a private vice has dependants whose welfare is not private at all. Feinberg did not think these observations destroyed the principle. He thought they showed that the principle could not do its work mechanically, and that each supposed instance of purely self-regarding conduct had to be examined rather than assumed.
Bernard Harcourt has pressed the point further, and less comfortably for the slogan's defenders. The harm principle, on Harcourt's account, has in practice collapsed under the weight of its own success. Because almost any conduct can be redescribed as harmful to someone (the redescription requires only ingenuity), the principle no longer screens out the paternalistic legislation it was designed to exclude. Legislators who wish to criminalise a self-regarding activity need only locate, or invent, a harm to others, and the principle that was supposed to constrain them instead supplies the vocabulary of their justification. The harm principle has not been defeated in argument; it has been absorbed, and an absorbed principle constrains nothing.
This is a genuine difficulty, but it is not a reason to abandon the principle. It is a reason to be more demanding about what counts as harm to others. Nina Peršak has argued that the principle retains its force only if it is coupled to a threshold: not every remote, diffuse, or speculative cost to others counts as the kind of harm that justifies criminalisation. A harm that is real, direct, and substantial engages the criminal law; a harm that is remote, diffuse, or conjectural does not, however ingeniously it is described. On this account the motorcyclist's call on public funds is precisely the kind of remote and diffuse cost that the threshold excludes, and the helmet law, if it is to be justified at all, must be justified as paternalism rather than smuggled in under the harm principle's respectable colours.
What follows is not the clean libertarian line the slogan promises. It is a more demanding and less tidy position. Where conduct is genuinely self-regarding, in the strong sense that any harm to others is remote, diffuse, or speculative, the criminal law should indeed stay its hand, and a society that criminalises such conduct is engaged in paternalism whether or not it admits as much. But the class of genuinely self-regarding conduct is smaller than the slogan supposes, because human beings are embedded in relationships of dependence and obligation that the slogan's atomistic picture ignores. The honest question is rarely whether the state may criminalise conduct that harms no one but the actor. It is whether a given piece of conduct really does harm no one but the actor, and that question is answered case by case, not by the recitation of a principle.
The slogan, in short, is not false. It is a placeholder for an argument it does not itself supply. To say that the state has no business criminalising purely self-regarding conduct is to say something true and almost empty, because the interesting disputes are never about whether purely self-regarding conduct may be criminalised. They are about whether the conduct in question is purely self-regarding at all, and on that question the slogan is silent. A criminal law worth having does not recite the principle; it does the work the principle only gestures towards.