to do a perfect scientific study of exactly how this virus would pass in the same exact envoronments with the only different factor being mask usage. Nobody can or will be able to prove this with some perfect accuracy. So what we really have is knowing this virus can and seems most often passed by aerosol and that expelling aerosol as well as intake is at least lessoned by a demonstrable amount by wearing masks.

There are other factors -- nobody is suggesting otherwise. But how in world can you possibly really believe that mask wearing does not serve as a logical mitigating factor? It just blows my mind.