In summary, countries spy on foreigners. Always have. Always will. That's exactly why we have an intelligence arms race developing. Country A spies on citizen

In summary, countries spy on foreigners. Always have. Always will. That's exactly why we have an intelligence arms race developing. Country A spies on citizens of Country B. Learns all sorts of useful information that could be used for doing some nasty things like black mailing political leaders, manipulating the economy, supporting anti-government groups, etc. Country B says hey wait a minute. Country A knows more about our our domestic situation than we do because they spy on our citizens and we don't. That could give them a huge strategic advantage. We gotta start spying on our own citizens to stay one step ahead of Country A! It's the evolution of warfare into the 21st century.