Of course it won’t stop virus particles, but it will stop aerosols, i.e. spit and exhaled vapors, which are present in asymptomatic people.
I don’t like it but the rationale is logical when people are required to be close together. Which is not in any retail store, if common sense is used. Getting a haircut is a case where masks would be appropriate.
I wear a mask every time I get a flu and have for years for exactly that reason. I don’t like the idea of making other people, maybe in worse shape than me, sick. If I’ve been wrong all this time, well, it hasn’t hurt me any.
Actually the wearer is breathing back in all of those expelled particles