Perhaps when we have one world government, it will make sense to have one world currency.  But, even setting aside the equilibrating benefits of flexible currencies, the prospect of a single, omnipotent central bank is not particularly appealing.
Tal vez cuando tengamos un gobierno planetario tenga sentido contar con una moneda mundial. Pero, incluso dejando de lado los beneficios equilibradores de las monedas flexibles, la perspectiva de un solo y omnipotente banco central no es particularmente atractiva.