Masks are imperfect BUT... they are better than nothing.

Multiple studies have shown that the DOSE of Coronavirus that gets you infected is important. The young people who had the worst outcome When they became infected in the initial wave were those who worked in healthcare, nursing home, or longterm care facilities, because the patients in those places were extremely susceptible and became very infectious and the people who worked there were occupationally exposed.

Young people with only incidental community exposure fared - in general - much better. Once infected, a race starts between the replicating virus and your immune system. If you are young the odds are against you getting a serious case in any event, but starting with a lower infecting dose means the immune system has more time to develop defenses against the virus compared to starting with a huge dose. With a small enough dose you won’t get infected at all - but most of us aren’t going to wear am M-17A1 or a filtered air supplied face mask, but if a simple facemask can decrease the infecteds viral fomites by half and the susceptibles facemask can decrease the inhaled virus by another half that is actually still worth doing. It might not stop the infection from occurring, but it will decrease the severity of the infection for the infected group as a whole.