https://www.npr.org/sections/health-shots/2020/06/21/880832213/yes-wearing-masks-helps-heres-why
The protection that masks offer is somewhat unclear. They might offer some protection to the wearer, and more protection to those around the wearer if he is shedding virus in respiratory droplets. Aerosols are much smaller and some get through, but I'd imagine there's a huge decrease in viral dose coming from someone wearing a facial cover as opposed to someone not wearing one, and I'd think that the infectious viral dose is somewhat correlated with the incidence and severity of disease, though apparently that's an open question.
So since a mask does offer some protection to the wearer, I'd guess that the unmasked morons walking around in public places are statistically more likely to have the disease, and therefore more likely to spread it also. If they were smart enough to realize this and made their own decision to wear masks, they wouldn't have to think the government was restricting their "freedom" by telling them to wear one.