When one doesn't know who has it and who doesn't have it, especially at ground zero, rather prudent for all to wear.
It doesn't hurt to wear one, other than diverting the supply away from critical frontline health workers. It does drive me crazy to see people with their surgical masks yet not wearing gloves and walking around touching everything in public like door knobs, hand rails, table tops, elevator buttons, etc. I'd be wearing gloves before a mask.
If I was riding NY subway, or city bus, or getting on a plane, or a cruise ship
, or working on a factory assembly line all day, I'd want one.