The moral cases are different, too. It should be self-evident that a foreign power’s violating your privacy and your own government’s doing so are by no means the same thing. For the vast majority of people, the practical importance of one’s secrets being obtained by one’s own government considerably outweigh the importance of their being obtained by a foreign power. The American federal government can and might do all sorts of immediate harm to me; the government of China, on the other hand, cannot. If a rogue official in the United States takes exception to my politics, he can make my life hell: inviting the government to track my whereabouts, ordering frivolous arrests, tying me up in endless audits and frivolous bureaucracy, and even sending a SWAT team to my house. If the Chinese politburo finds me objectionable (and I certainly hope it does), it can do very little of practical importance. Moreover, and this I think is the key point, if China tries to actually hurt me, I have distance, borders, and the American government’s considerable arsenal standing in the way. If someone at home tries to hurt me, I have little individual recourse.
For as long as the world features international borders, it will be one thing for federal guns and listening apparatus to be pointing outward — protecting me from foreign foes — and quite another for them to be directed inward. The world has shrunk somewhat since the Founders’ time, but the validity of their belief that the domestic use of troops and force presents a threat to liberty has not. Thankfully, the internationally peculiar Anglo-American expectation that the national government may deploy troops anywhere it wishes outside of its borders but must not use them at home remains in legal force courtesy of the Posse Comitatus Act and in moral force courtesy of an ongoing American distaste for government intrusion. There is no reason that we shouldn’t demand that our sleuths hew to the same principle. (While we’re at it, we might also see fit to push back against the increasingly common sight of hybrid soldier-cops and military-grade SWAT teams, as documented by Radley Balko in his brilliant book Rise of the Warrior Cop, thus ensuring that we do not allow in a domestic standing army by another name.)