Final answer:
The argument that all EU members should not necessarily join the Eurozone due to potential widespread instability caused by individual country's economic difficulties is strong. It highlights the loss of domestic monetary policy control and the possibility of contagion effects within the Eurozone.
Step-by-step explanation:
The question of whether all members of the European Union should join the Eurozone and adopt the euro is complex. The argument presented states that instability in one Eurozone country could cause the whole zone to become unstable, affecting all member economies. This argument is considered strong because a merged currency eliminates domestic monetary policy control, placing decisions in the hands of a supranational institution like the European Central Bank.
Such centralized decisions may not always align with the economic needs of individual member states. Furthermore, the interconnected nature of the Eurozone implies that economic challenges in one nation can quickly spread to others, disrupting the stability of the entire region.