Don't pretend that Germany didn't benefit hugely from the economic integration of weaker countries such as Greece. It takes two to tango, and tango you did.
The single currency tied the economies together, it allowed Greeks to use the cheap credit of the German economy to buy what? German cars. Germany's export businesses grew hugely because of the real value of the euro was weaker than the Deutsche Mark.
This is a problem where no single party is at fault. Yes, the Greeks were irresponsible with the credit but it's not the full story.
Apart from that, I agree with your points about the general economic union. Without a peaceful political and cultural one, it was doomed to fail.