Never forget that the last last group to organize and act violently against the Postal Service was, in fact, YPSL. Then, there's a history of this nonsense back in the early 1900s where members of organizations which are predecessors to Rosenburg's and of YPSL, were actually out tossing bombs in post offices, blowing up postal wagons and trucks, blowing up trains, etc.
(And why do I suddenly feel like "Egan, 40-41"?)