Let's get things straight about facemasks.
Your run-of-the-mill face mask does NOT protect the wearer very much at all. Most of the air you breath while wearing such a mask comes in from the edges of the mask and is no different from the air you would breath without a mask. Very little air is actually filtered through the mask material.
So, what good are they? Well, consider that a surgeon does not wear a surgical mask to protect himself, but to protect his patient. Masks are pretty effective at blocking the spray we all make when speaking, singing, coughing, and sneezing. It is this spray that carries viruses and bacteria and the spray is effectively blocked by a mask, or even a bandanna. The illustration below shows how well a face mask blocks bacteria spread from spray. The same thing would go for viruses.
There are N95 respirator masks that are fitted to your face so that a built in filter cleanses the air you inhale. These masks will protect the wearer from ambient infectious material, but they are specialized masks that you don't buy at the local store.
Therefore, it is recommended that we wear masks in public, especially indoors, to protect OTHERS from your potentially infectious emissions. "But, I am not sick and don't carry the virus." you say. That is the thing about this virus. Many people do not know that they are infected and walk around spreading their viral joy without knowing it. So, it is recommended we wear masks for the sake of others, including people at high risk for serious disease.
It was recently reported in these pages that if 50% of us wore masks in public, the transmission rate of this virus would drop 70-80%. The infectability number, called R0 by epidemiologists, would drop from about 4 to <1, which is the goal for reducing the spread of any infectious disease. We could dramatically hinder the further spread of this virus without a vaccine or drug, simply by wearing facemasks.