Good post. It is a different way of looking at your role in society. It always surprises me that people do not realize that the people you see wearing surgical masks during flue epidemics in Japan, are wearing them to protect other people from the infection the wearer thinks he or she may have.
It definitely goes both ways. Yobou is a big thing over here. It means prevention. You are right, if a person thinks he/she is sick, he/she will often wear a mask out of courtesy to others, so as not to get other people sick. Likewise, when illnesses are going around, it's very common to see people wearing masks to protect themselves. Many places in Japan have dense populations and illnesses like Influenza spread very quickly. Thanks for all of your comments!