Driven by data; ridden with liberty.
John Stuart Mill’s harm principle in On Liberty is a crux of classical liberal and libertarian politics, as it serves to guide when a government or society should take action. The harm principle is also very useful in organised debates, as it generally ensures that the speaker has mentally performed a stakeholder analysis – that is, a consideration of who is affected by new laws and how they are affected. Mill states:
The object of this Essay is to assert one very simple principle, as entitled to govern absolutely the dealings of society with the individual in the way of compulsion and control, whether the means used be physical force in the form of legal penalties, or the moral coercion of public opinion. That principle is, that the sole end for which mankind are warranted, individually or collectively, in interfering with the liberty of action of any of their number, is self-protection. 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. His own good, either physical or moral, is not sufficient warrant.
The violation of Mill’s harm principle is a necessary, but not a sufficient, condition for a response. There are two complications with this simple principle: the constitution of harm and the potential of accumulated harm. Modern ‘harms’ comes in various garbs, such as physical harm, financial losses and psychological scathes. This widened definition often results in the citation of the harm principle in the exact manner which Mill opposed: laws against hate speech.
Mill vociferously rejected such laws, arguing:
If all mankind minus one were of one opinion, and only one person were of the contrary opinion, mankind would be no more justified in silencing that one person than he, if he had the power, would be justified in silencing mankind.
The harm principle is intrinsically challenging when considering accumulated harms. This was particularly pertinent when discussing legislation to ban the prevention of smoking in cars with anyone under the age of 18. This law would punish the driver for a single instance, when the single instance of being in a car with a smoker is only negligibly harmful, though I personally find it unpleasant. The physical harm from second-hand smoke comes from long and repeated exposure. A 2013 study published in the Journal of the National Cancer Institute found the only category of never-smokers that experienced a clear association with lung cancer were those “living in the same house with a smoker for 30 years or more”. Similarly, giving a child some cake for their birthday is a pleasure, but giving them cake every day for years is somewhat unhealthy.
If you are classically liberal, then banning smoking in cars with children might be an application of Mill’s harm principle. There is an inherent problem, when considering negligible harms in single instances that become severe through repetition. I see no dishonour in erring on one side when children are involved.