Doing the work the authorities won’t do. Not the vigilante’s fault, it’s the authority’s.
That’s why, inevitably, when the authorities are impotent and feckless, vigilantes pop up like mushrooms after the rain. It’s not a good situation, but it is a natural consequence of an impotent, feckless government.
Think Death Wish. Charles Bronson made a fortune off of the dramatization of this concept.