In terms of microeconomic point of view, the common currency is beneficial to trade between companies across the border.
Nonetheless, the common currency does not imply the free market. The beneficiality of introducing a common currency in the EU is that the trade frequency between countries in the EU is significantly higher than the USA. However, the labour mobility rate between countries in the EU is significantly lower than the US counterpart.
It is not fully proven yet whether a common currency leads the economy to have a high trade frequency and the labour mobility across the border or these factors require introducing a common currency.
If the statement "Free market demands common currency" is valid, it should be that both the trade frequency and the labour mobility have been high before a common currency is introduced, and then a common currency should be introduced afterward. However, if the reason to introduce the common currency is to "expect" the trade frequency and the labour mobility to become high after introducing the currency, the aspect does not fulfill the natural mechanism of the free market. Under the free market, needs induce the supply; expectations are not necessarily relevant to induce the supply.
Under the current European situation, although the aggregate level of trade frequency across the border is high there are a few countries which do not fulfill the condition such as Ireland and Greece. Furthermore, there is a huge barrier of introducing a common currency under the free market principle which is the labour mobility. If the EU situation is that the free market demands the Euro, the labour mobilty should have been much higher than what the EU has got.
All in all, I would like to strongly put emphasis on the statement that both the EU and the USA do not hold their own single currency used among their own states or countries inside them due to the free-marketism.
For example, as a matter of fact, the USA should abandon the single currency system and her federal government interaction into her market if she wants a free market! The US market has a significantly lower trade frequency across the borders between her countries than the EU and Asian economic regions. The current US situation craves for the strong federal planned economic intervention in order to stick these individual states with being the United States of America!!
In order to accomplish to estabilish a free market system, abolition of nation states is necessary in order to allow all individual regions to become free from any planned economic intevention. Overall, nationalism and unionism never go well together with a free market! "Anarch-Capitalism" is only the answer to support free market!!
