Shutting down Bitcoin would be a simply matter of throwing some money at the problem. Shutting down Citibank would require a legal fight.
A legal fight is a matter of legislation. Should the laws shift within a nation, it becomes easier to shut them down, contrary to Bitcoin, which adheres to the immutable laws of mathematics and physics. Regardless of its legal status in any given country, Bitcoin persists as a force that requires billions of dollars to suppress.
As I said above, Bitcoin is, as a whole, probably easier to attack than a large American bank.
I believe the comparison to an American bank is flawed. Unlike a bank, which readily shares identifiable information with the government upon request, you operate as a company issuing custom currencies. If these currencies facilitate anonymous transactions beyond your tracking capabilities, you're essentially conducting operations beyond the government's oversight. Eventually, you'll be viewed as enemy to them, and if that happens... bye-bye Haypenny.