[shadowgovt]

I'm not very certain that a nation of 350 million people can be kept stable without some amount of internal espionage.

Most human constructs of that size have espionage going on between them (for example, that's more than the population of Germany and Russia combined, and those nations are definitely spying on each other). The fact that they have a thick border drawn on the map between them and the US has thin borders drawn on its map probably implies the US should spy on itself less... But how much less?

Internal espionage has been key at several points in the history of the US for preventing internal power structures from overriding law and order (the Chicago mafia, for example). It has, obviously, also been leveraged against the rights of law-abiding citizens.