TerryL,
Establishing a single world currency will not be easy. Do you think US will give up dollar hegemony just like that? If US government rejects the option of oil valuation in euro, then such dream as giving up dollar hegemony is just too far from reality.
Combining different currencies into one also difficult in terms of uniforming the monetary policies across countries, and interest rates as well as accounting and budgetary systems across the globe will have to be melded together.
Just look at the EU. There are still members that breach the budget rules there, even after euro existed for several years now. And that is to mention EU is still a regional organization.
People each thinks differently. Each has different visions and ideals. These differences are at most occasions, conflict each other. This is why unifying ideals and visions across the globe is virtually impossible for now. Universal currency requires such thing before it could be realized.
Fixed exchange rates and floating ones are similar to monopoly and free markets. Most people prefer free markets, which could be translated to "democracy" and "freedom", while monopoly translates to "authoritarian". Under fixed exchange rates, some currencies may get themselves overvalued or undervalued, and this demand a solution which I think will be difficult to find. Under floating exchange rates, the market decides the value of each currencies, and thus there's hardly any overvaluation or undervaluation occur. There are times when speculative forces create extreme conditions that lead to overvaluations and/or undervaluations, but in time, this will be sorted out by the market as the price will tend to re-balance itself. I guess this is also an obstacle to achieve the creation of a universal currency.
As for why the poor gets poorer or the rich gets richer, that has nothing to do with money. Even rich countries began as nothing. Such way of thinking will only reinforce the imbalance. Currently poor countries still have resources, natural resources. These countries may have been exploited by rich countries, while they actually have the right to say "no". So, why don't just say "no"? Why would their governments yield to the will of the rich nations? Interests have nothing to do with such situations.
You don't like interests? Don't accept them, then. To my view, interests is how we compensate inflation rate. The nominal amount of money plus interests rate minus inflation rate is your real amount of money. Erasing interests will reduce your real amount of money. Unless the economy suffers deflation. But nowadays, prices of goods move up, not down.
That's all I want to say for now.
Cheers!