The Dollar is worthless too, it derives it's value from the movement of goods done with it. It is merely a measure of transaction. You could almost say that when a currency goes beyond it's intended connections it becomes extremely manipulative of those territories it imposes on. by accepting a particular Currency one is aligning oneself with it's development, to be taken into account as one of it's working participants... at the same time it introduces a weakness as it's over-reach could trigger a negative spiral by being abandoned by those who hold no allegiance to it's claims.