What specific harm is being done here though? Krugman has a tendency to take a lot of underlying assumptions for granted without actually enumerating them. I’m looking to understand why Germany should have to manage its economy based on the aims of the rest of the EU and not their own, which seems to be what’s implied here.

“* I’m looking to understand why Germany should have to manage its economy based on the aims of the rest of the EU and not their own*”

Because Germany has renounced part of its independence and sovereignty by joining the EU, so now it has to do the patriotic thing and think of that larger collective. As a point of comparison, should New York do what is best for New York, or what is best for the country? At least sometimes, we expect New York to sacrifice its own interests and do the patriotic thing for the whole country. As was pointed out many times during the crisis years of 2008-2013, many of the problems in the EU exist because of its partial and unfinished integration. It is very difficult to have a unified currency without also having a unified fiscal policy. As others have pointed out, the EU cannot survive in its current state, either it breaks up or it deepens its integration and becomes a United States of Europe.

>Because Germany has renounced part of its independence and sovereignty by joining the EU, so now it has to do the patriotic thing and think of that larger collective.

Is this enumerated in a treaty? Which law says this?

>As a point of comparison, should New York do what is best for New York, or what is best for the country? At least sometimes, we expect New York to sacrifice its own interests and do the patriotic thing for the whole country.

I live in the United States and I have never, ever, heard of this question being asked. Which thing is New York sacrificing for the rest of the United States?

Yes, there is a maximum allowed limit in the Maastricht treaty. Germany has been systematically breaking the rules.

https://www.intereconomics.eu/contents/year/2018/number/3/ar...

"The rules established under the EU’s macroeconomic imbalance procedure (MIP)define a ceiling for current account surpluses of six per cent of GDP and stipulate that the three-year average for a country’s current account surplus should not exceed this ceiling.2 However, Germany has been running surpluses in excess of this figure for many years. Its most recent three-year average is eight per cent of GDP, while the 2016 figure was even higher, at 8.5%."

Put simply, Germany wants (or wanted - we don't talk about the euro crisis much anymore even though it was never really resolved) everyone in the EU to a) trade mostly with other EU members, b) run a trade surplus. This is obviously impossible, but Germans don't want to hear that in a modern economy, for Germany to have no debts means someone else must. They sent moralists to do an economist's job.

That being said I have no idea what the OP was on about, it's not illegal, it's just stupid.