Even assuming - let's say for sake of argument - that masks ARE useful to protect against Covid. Both the wearer and the others surrounding them ok?
There are so many different types of masks made of a wide range of different materials. Some masks are perfectly safe while others are bound to be dangerous.
You shouldn't wear a mask while exercising. That is a given that we all can agree on.
Now define exercise.
For me running up the stairs I don't even get winded but I'm 6'/155~160lbs.
Up until a few years ago I could jog a few kms and only barely get winded or break a sweat. Now I work a more sedentary job and it's slightly degraded (and also age I suppose) so that I can jog but after a while I get winded and my heart races and of course my ankles, knees, etc will hurt.
Now take someone that eats cheetos and plays video games all day. I sold an Xbone to a very nice young man last winter. He was very overweight, like the youth was about 5'9"/300lbs. Maybe more. He had trouble getting DOWN the stairs to my basement, that is 6 steps. He then struggled to get onto a Poang (ikea) chair to test out the console before buying it.
He was out of breath. Now, send this guy to the grocery store and make him wear a mask = disaster waiting to happen.
And we all know that all Americans are fit. (NOT!)
My personal take is the reason for our nostrils to have evolved to the size/capacity they have is to be able to supply air to our organism. We have been provided a nice filter by mother nature under the form or tiny hair that protect us from viruses and other crap, these hair have a "motion" that sweeps crap up and out. That is why your nose runs and you cough up shit, it's normal, it's your body expelling bad crap.
I'm not going to say this protects 100% against Covid that would be preposterous. But the masks for everyone may be overkill right now. They should've been mandatory at the start but then in March, they didn't have dozens of display cases all over department stores stocked with thousands of masks.
Why make them mandatory now? IMHO health is the least of the reasons behind politics, workers unions, associations, etc.
There's my interpretation.
TL;DR
There are too many variables to make a claim as to whether masks are safe and should/should not be worn.