Final answer:
The argument is weak because the European Union allows for member state sovereignty, including the choice to retain their own currency. A single currency entails giving up control over national monetary policy, which may not align with every country's needs. Moreover, several EU countries have consciously chosen not to adopt the euro, indicating a preference for maintaining national monetary autonomy over the potential benefits of a common currency.
Step-by-step explanation:
The argument that all members of the European Union should join the Eurozone and adopt the euro is a weak argument. The European Union (EU) is designed to accommodate a range of member state preferences and varying levels of integration. While many EU countries have indeed adopted the euro and participate in the Eurozone, the EU recognizes the sovereignty of its member states, which includes the right to maintain their own currency if they choose.
Adopting the euro comes with benefits, such as eliminating currency exchange costs and fostering closer economic ties. However, it also means relinquishing control over national monetary policy to the European Central Bank (ECB). This can pose challenges for individual countries, like Portugal, whose optimal monetary policy might differ from the one set by the ECB.
Furthermore, certain EU members like the United Kingdom (prior to Brexit), Denmark, and Sweden have opted to keep their national currencies. These decisions underscore the notion that a one-size-fits-all approach does not necessarily serve the interests of all member states. The EU values diversity in its membership and provides a framework for different levels of integration, reflecting different economic structures and political preferences of its members.