Last week, presumed Democratic presidential nominee Joe Biden called on state governors to order residents to wear masks in order to reduce transmission of the SARS-CoV‑2 virus.

According to UPI:

“Every single American should be wearing a mask when they’re outside for the next three months at a minimum,” Biden said. “Every governor should mandate mandatory mask wearing.”

It’s unclear what significance his statement has beyond virtue signaling. Still, the idea has popular support; a recent Fox News poll (see question 40) finds that 74% of respondents support such a requirement.

Mask-wearing, of course, is important in this pandemic. As I note in a forthcoming paper on limited government and COVID-19, there is scientific consensus that infected people (who often are unaware they’re infected) who wear masks greatly reduce the odds of their infecting others. There also is growing evidence that uninfected people who wear masks reduce their risk of becoming infected, though not as much as when the infected wear masks. And when both the infected and uninfected wear masks, risk of transmission appears to be extremely low, especially if they also practice social distancing.

In policy terms, SARS-CoV‑2 is a negative externality: a cost involuntarily foisted on others. Limited government can (and in many cases should) address negative externalities, subject to such restrictions as that the resulting policies do not infringe on protected rights and do provide net benefits to society. Requiring the wearing of masks appears to be such a policy; it certainly seems at least as legitimate as largely uncontroversial public decency laws requiring the wearing of some clothing when in public.

And yet, Biden is wrong that governors should require U.S. residents to wear masks whenever they’re outside. Many times, when people are outside their homes, they do not put others at involuntary risk of infection. From hiking and biking on public lands, to boating and fishing public waterways, to driving on public roads, to outdoor activities on private property (but not at home), and countless other instances, there are plenty of instances where mask-wearing creates little or no involuntary risk of infection. A general mask mandate would thus produce countless government failures.

Statewide mask mandates would both violate the principles of limited government and cause unnecessary harm to citizens. As I explain in my paper, mask policy should be left to local governments (a point that applies to both Biden and to Georgia Gov. Brian Kemp and Arizona Gov. Doug Ducey, both of whom at one time prohibited local mask ordinances). At the local level, policymakers are more responsive to citizens and the ordinances can be better tailored to address specific circumstances—including, perhaps, cases where there is no community spread and no need for masks.