Except for a lot of damage to goodwill, which can have an economic impact. Lots of European citizens dislike the US heavily now and that comes with disliking US products.
Your political decisions therefore will have an impact on the effectiveness of our military system to defend our country.
First, the US and Germany are allies. Allies talk and don't spy. Second, by now it's clear that a lot of the espionage is economical.
The US/NSA mistreated their allies. It will take many years to rebuild trust.
If you want to figure out a world where people aren't self-interested and risk-averse, maybe a church would be a better place for you to have that discussion.
And I agree that most if not all decisions are based or should be based on the expected gain, but the question is then of course how you define or measure that gain. There may actually be a real gain for a country if you spy on other countries, but I argue that this is the wrong standard for gain in that situation, a selfish definition of gain. I would strongly prefer to consider the gain or loss for the whole world when evaluating decisions like whether or not to spy on other countries.
The point seemed to be: "just because it has a pro, doesn't mean I should do it". I could use the same logic to state that I can only gain by spying on my friends as well. Does that mean I should? Does that mean it has no downsides?
The economic espionage side I'm much less happy about.
And I see neither how something we decide in Germany may affect the UK to a degree that justifies espionage, nor do I see how decision of the UK may impact Germany to such a degree. Can you think of a good example?
And if you see how nothing in Germany could be decided that affects the UK, what do you think would happen if German and French banks had refused to fund bailouts for the less responsible EU companies? No effects felt outside of Germany?
And I did not say that the decisions in Germany (or any other country) can not influence the situation of other countries, I said they can not influence them to a degree that justifies espionage. So how does you example apply? Germany and France are free to support or not support what ever they want. How would having known such decisions before they were publicly announced made any difference?
Besides, the prisoners dilemma assumes there are no penalties for betrayal and that certainly is not the case for international politics.
[1] https://en.wikipedia.org/wiki/Prisoner%27s_dilemma#The_itera...
The last sentence is where he is - only in my opinion of course - completely wrong; no country should spy on other countries without very good reasons. And wanting to know what is going on behind closed doors of foreign governments or companies misses my definition of very good reasons by orders of magnitude.