In that case I think it was more a matter of Japanese society frowning on public displays of physical affection.
As I understand it, the human body needs to be sick to build immunity, but it also is specific. Having the flu repeatedly will most likley not protect you from getting chicken pox and vis versa. Once you have had chicken pox though, the chance of you contracting it again is almost non existent. Even having dealt with one type of flu, your immune system may not necessarilly protect you from a different strain of flu.
I believe the human body was meant to get sick. By preventing all the minor illnesses you are denying the bodys immune system the chance to adapt to changes in types of sickness going around thus setting yourself up for a massive illness that your immune system is totally unprepared to combat. Unfortunatly since viruses mutate thru their environment, our ability to quickly travel the world does the same thing in providing us access to illness that our body is not familliar with. History has proven this over and over. Columbus discovering the new world and European settlers colonizing the Americas caused massive death rates in the native populations from new illnesses untill their immune systems adapted. Any guesses to the biggest killer during the first world war? If I recall my history correctly, it wasn't combat...