Hit the nail pretty much exactly on the head here.
So effectively double the overhead of running an econ department in a lot of areas. This rather significantly hurts wartime/rebuild management and Dio forbid you try running a command economy. If you legitimately feel this is bad for the game you should petition Alex to make bank theft against the rules outright. That being said I agree with Lariah and the Hippo, bank stealing is a valid tactic, just ask kastor. This is ultimately a war game and there should be no assurity of safety in anything.