To me, vigilantes are the people who raid the local jailhouse to accomodate those who apparently need stringing up -- not honest citizens who accept the task of self-preservation . . .
If you search the "Wall Street Journal" (early 80's) you'll find an article which describes good samaritans with 'illegal' sidearms in NYC who, like 'Zorro', appear suddenly to foil bad men, then 'dissapear' into the crowd. These responsible armed (albeit contrary to NYC regs.) citizens were credited with making the streets safer for the residents of the city -- and probably still do.