Monetary union means the loss of sovereignty, because the state is no longer definitionally solvent and can thus not engage in a number of tasks conventionally considered a requirement for sovereignty (such as domestic macroeconomic planning).

As well as

• deposit insurance for banks
  
• granting limited liability to businesses
  
• disaster relief
  
• access to health care
  
• access to education
  
• access to legal redress
  
• public safety
  

In other words, monetary union leads to failed states. Greece, for instance, wasn't one three years ago and may well be one a year from now.

There are three stories about the euro crisis: the Republican story, the German story, and the truth. -- Paul Krugman