I believe you need to first define the risks and realities carrying a banned knife whether it be during normal times or an emergency.

1) I could be mistaken, however during and after 9/11 and the 2003 power blackouts there was no real increase in crime (aside from some looting) such as muggings, robberies etc. All the news I seen and heard were of people like you who just wanted to get home.

2) To carry a knife and to effectively use it in self-defense are two completely different realities. Although you have a martial arts background, it no substitute for essentially what is hand to hand combat fighting with a knife. Also a previous poster mentioned about the risks of bodily fluids..that to me is almost enough deterrent.

3) Is there enough crime in your area that carrying a knife in Massachusetts is worth the risk of getting caught with said knife in normal times, let alone during an emergency when authorities would even be more vigilent. According to this website the laws and penalties are quite strict and draconian in your state.

4) In any urban or rural environment, I think that you could find a lot more effective self-defense options that would serve a better purpose then a knife.