I think masks are a great way to show the spread of disease in many environments. But sometimes they don't make sense or do more harm than good, which is why I think it should be strongly encouraged but left up to individuals and establishments to decide according to their needs. 

For instance, grocery store workers with long shifts tend to constantly touch and adjust them, move them to their chin, etc. They are constantly touching people's things after touching their mask and face and that makes it more likely they will spread disease through touch. But masks are not to protect the wearer. In this case the mask does more harm because they contaminate groceries and the customer is only in contact with them for a few minutes and is often behind a plastic shield. 

Customers, on the other hand, are on the store awhile and in contact with lots of people. It's better for customers to wear masks to protect the store workers.  

Children--especially in schools--should not have to wear masks either. They also constantly touch and adjust them without washing their hands, and are more likely to have behavior problems  due to low oxygen and to be distracted by the masks. 

Exercising is dangerous to wear a mask. Outdoors it isn't really necessary unless you are in a crowded area. 

I think focusing in improving ventilation in enclosed spaces would be a great to to help masks may not make sense.