Says who? You? I'm sure you've probably provided one already, but post me a link to this study because I haven't seen it.99.9 percent of transmission is from touching your face, not through the air. Dirty masks are of no help.
But lets just say that is in fact the case....
In the immortal words of Mr. Jules Winnfield...
"Allow me to retort".
How does it get on peoples hands?
Oh from surfaces?
And how do you think, it gets on those surfaces B!?
Air maybe?
Oh... people touch their face and then touch a door-knob?
That's the dumbest thing I ever heard. That's some serious face touching.
And dirty masks? Dirty from what? Inhalation or exhalation?
Inhalation, you're going to breath it anyway; exhalation, I really don't think I am breathing out anything that's going to make me sick. Again, a dumb argument based on nothing.
Besides, the cloth ones can be washed, paper disposed of, and the good ones can be soaked in Hydrogen Peroxide and dried.