Bitcoins can easily be stopped. If Bitcoin sees steady adoption and abuse is not widespread it can probably coexist with, and gradually take some market share from banks. If it continues it's current militant/illegal approach it will be gone fairly quickly.
Easily be stopped? Hardly. You have to realize that the government is slow to react. Even if the US outlaws bitcoins or another countries does then there are still 200+ other countries where it is legal. The bitcoin economy in those countries could still be growing and it might get to the point where the US wants a piece of this action so they legalize bitcoins again.