A single currency is a bad idea. As you know markets are driven by the cost of goods and services, operating supplies and management. They are supported by a nation's value systems which materialize into economic theory and practice. Well, you've heard that "too many cooks spoil the broth?" Each world entity, government and nation should govern themselves with common virtues, values and  currencies of their own in front of the world community. When we would collectively bargain and support our common economy with a common currency, we would also fall prey to the negative economic effects of other member shortcomings, political setbacks and transparency in government would remain a contention.

The world economy is collectively driven by its member nations as is. However, to make it a single identified currency would be too unstable, its setbacks more frequent, and the authority to govern would be politically driven. The idea, that the EU has of transferring authority is good,but even with the rotation of authority people are subject to the ideas, values and incentives that are  out of their reach. For the common man, the governing of many member nations amounts to price fixing and support for an underground economy at its worst. However well intended at the end of the day the potential for instability is too great.

Common currency worldwide would be too vulnerable and frenetic this way: people would destabilize the currency easily by changing the import/export policies of their member nations. Why do you think that the English are not in on the EURO?

Because it would subject their potential for operating a flourishing, an independent and a successful and lucrative economy to other economies and setbacks. Each country should have their own currency...I'm firm on that.