I think Kate's other point is right on. Politically, what you are asking law enforcement, etc. to do is to become less effective for the sake of people's privacy. You can argue that the trade-off is too great, or that the agencies forced behind the screen would not actually lose effectiveness, but all it takes for a counter-argument is a single publicized event that could have been avoided by information sharing. I think it is too easy for the powers that be to point to a murder or child abduction and say, "we would have been able to stop this if we had access to more information." The dangers of the slow erosion of privacy are difficult to paint in such concrete and effective terms.

-- TheodoreSmith - 22 Feb 2009