I see your point, but someone else wearing a mask in public doesn’t harm me in any way.

I can also envision a number of situations where someone may do what you are describing but be immune compromised (from chemo for instance) and simply not want to live their life as a shut in.

A mask, even if improperly worn, still might offer such a person the motivation or (even false) sense of security to get out in the world and experience what little of life they can.

I say more power to them.