Evidence from the Virginia Department of Health shows at best an ambiguous relationship between mask wearing and COVID-19 cases. Average case numbers were falling precipitously before the onset of a mask mandate on May 29. Since the mandate the average has climbed back close to its pre-mandate peak.
Evidence from a study of 24 countries and 25 states shows a similarly ambiguous relationship between state interventions and COVID-19-related deaths. They differed wildly on whether, when, or how strictly governments intervened, but their experience is almost identical. The ambiguous effect of interventions should induce humility that any particular intervention, such as mandating masks, “makes the difference."
Masks should be optional because they are primarily meant to protect the wearer. This is natural and historically the case. If you doubt this try to think back a year ago. If you saw someone wearing a mask in public you intuitively knew they were trying to prevent against something from the environment — allergens, viruses, pollution, etc. — getting into their system.
There are costs to having everyone wear a mask. The inability to see faces has been linked to rising anxiety. Learning to read facial expressions is one of the first things a baby does because it is one of the most critical skills necessary for survival. People show their emotions on their faces, and from long before humans could speak we needed to to tell anger from deceit from joy.