A: If the U.S. really wants to get tough on vigilanteism, then it's not your masked-and-costumed hero they should be cracking down on. It's the gangs of teenage youths who roam the countryside in vans with anthropomorphic animals, solving all kinds of crimes without any kind of federal or state mandate.
B: You say "all kinds"...
A: Well, admittedly they're usually the type of of fraud which entails dressing up as ghosts, vampires or some other form of monster in order to scare people away from whatever secret the criminal wants to stay hidden, like an altered will or stolen deeds.
B: Or a newly-discovered gold seam?
A: Well, quite. I wonder why crimes like that are so prevalent in the rural U.S.A.?
B: Just their equivalent of muggings and petty thefts, I suppose.
A: You'd think the government would do something about it. Make impersonation of a creature from folklore or the horror genre for personal gain a federal offence.
B: You would, wouldn't you?
A: I wonder why they don't?
B: Pressure from the Trick or Treat lobby, I guess.