If you are infected and you cough, the mask catches it.
If you don't have it and someone coughs near you a mask will diminish the amount inhaled, reducing the chance of it taking hold before the immune system takes care of it.
Demonstrable and repeatable.
You can quote Sweden all you like, but it ignores the idiosyncrasies of that country in favour of painting it as a magical country where they won by using their freedoms.
Basically, Sweden is a lower-density population with a culture of not being in each others' face among other differences.
Distancing > masks, which is why you don't see concerts with masks. Sweden went without, with mixed results. Other places aren't Sweden, and masks are more necessary. Refusing to wear one usually either comes with a denial of science or the word "Freedom".
Not exactly the numbers of a magical solution who proves anti-maskers right.
It's so simple. Stay away when you can, mask for when you can't.