The Cliffs Notes version is a face covering is only going to help stop spreading virus particles that get sprayed out when a person with the virus coughs, sneezes, speaks, or exhales.
If they’re coughing or sneezing they shouldn’t be out in public. Same thing if they know they have the virus but aren’t symptomatic.
Whats left is asymptomatics who don’t know they have the virus and would other wise unknowingly spread it. Which is a very small fraction of the population.
And even if they did, there’s the question of viral load, i.e. how much exposure does it take to actually get the disease? Contact tracing standards were less than 6’ away for 15 minutes, so it takes more than passing someone in a grocery store aisle.
Some exposure is necessary to develop herd immunity and masks slow that down. Since no one has developed a vaccine for any coronavirus yet, natural immunity may be the best we ever get.
But masks will be touted by the media as virtuous, and those who don’t wear them (aka Trump supporters) are evil. The message is “wearing a mask saves lives” and failure to do so is racist (or something).
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Whats left is asymptomatics who don’t know they have the virus and would other wise unknowingly spread it. Which is a very small fraction of the population.
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From what I have read it is not for sure that asymptomic positives can pass the virus to others.