Emmel, the NSA spokeswoman, told the Guardian: "Current technology simply does not permit us to positively identify all of the persons or locations associated with a given communication (for example, it may be possible to say with certainty that a communication traversed a particular path within the internet. It is harder to know the ultimate source or destination, or more particularly the identity of the person represented by the TO:, FROM: or CC: field of an e-mail address or the abstraction of an IP address).
Basically the NSA is arguing that since they can't be 100% sure of the actual person reading email addressed to that person, then they aren't invading the privacy of that person. Such an argument would be laughed at in any court of law.
There are no doubt plenty of areas that require attention and correction. I will not vilify the NSA, however — which is not to say I’m endorsing the exposure of privacy.
The threats exist. They must be identified. Something should be done to isolate identities requiring warrants for exposure. Since Congress is a complete failure on this matter, a private sector consortium should be established to help balance the concerns of privacy with security.