Pose serious health risk to the healthy.
It’s definitely a bad idea to exercise wearing one.
The infuriating thing about this is the inability of some people to understand that there are no risk-free actions, or to accuse people who think that destroying the economy is sort of a bad idea of wanting grandma to die. They act like children.
[Update early afternoon]
The uncertainties of mask use demand that no one be forced to wear them.