John Stuart Mill and the Contagious Diseases Acts: whose law? Whose liberty? Whose greater good?

Legal fictions are often used to lubricate the machinery of jurisprudence. One of these is the idea that laws created to restrict the liberty of some individuals or class of individuals in order to protect the public good are in effect outcomes of tradeoffs between abstract universals, namely liberty and the public good. A three way relationship is imagined in which law, liberty, and the public good are in creative tension. The role of the law in this three way tension is further imagined to be the mediator where it serves to calibrate this tension in ways that are also assumed to legitimate the intended outcomes in practice. In particular, where the outcome is the prevention of harm, then laws that curtail liberty must be seen not just as measures for the public good, but rather as necessitated by the potential effects of the very harm itself. The justification for this view is often traced back to the views of nineteenth century political philosopher John Stuart Mill, who famously expressed this in terms that have become known as the “harm principle”; specifically that “the only purpose for which power can be rightfully exercised over any member of a civilized community, against his will, is to prevent harm to others.”