Some viruses would go through some masks the way water goes through a strainer.
The minute you start to perspire...most of the cheaper-made masks are worthless.
Reminds me of what a WWI commander instructed his men to do to their handkerchiefs during a gas attack.
Almost all viruses will easily pass through masks. What you are missing is viruses do not float free in air. They are suspended in tiny moisture droplets. Those droplets do not pass. In the cold and low humidity of winter those droplets are smaller and suspend in air longer, hence winter flu. Even the small winter droplets do not pass masks. Masks are better at preventing spread out rather than in.
Without a mask those virus laden droplets lodge in the mucous membranes of the nose throat and lungs. Without eye protection they lodge in the eyes and some (Apparently Corona) can spread that way too.
The probably bigger benefit of masks is they prevent you from subconsciously touching your mouth or nose. (3 times an hour on average) The surface to hand to mouth or nose or eyes transmission route is usually a more efficient way to infect someone with a substantial viral load.
Virus has also been found in urine and fecal matter so avoiding public bathrooms like the plague (pun intended) is highly advised. (Flushing aerosolises what is in the bowl/urinal)
Gloves, goggles, n95 masks, throwing our clothes in a dryer for 15 minutes on hot, an immediate shower and good hand disinfection after being out is about all we can do.