Final answer:
The argument against all EU members joining the Eurozone and adopting the euro as a result of adaptation challenges and loss of monetary policy control is considered strong. It reflects the significant impact on the sovereignty and economic policies of individual member states.
Step-by-step explanation:
The question asks whether all members of the European Union should join the Eurozone and adopt the euro as their currency. The argument provided suggests that it may be difficult for countries to adapt to a new currency, and it poses a potential loss of monetary policy autonomy for individual nations.
For example, when Portugal is part of the Eurozone, it must adhere to the monetary policy set by the European Central Bank, which may not always align with what a Portuguese central bank would decide. This can be seen as a strong argument because it addresses the significant sovereignty and economic policy implications for member states. It considers the fact that a merged currency, like a hard peg, means relinquishing control over domestic monetary policy, which can be crucial during economic fluctuations unique to a country.