Writing for Wired Wednesday, Matt Blaze, director of the Distributed Systems Lab at the University of Pennsylvania, lays out the best explanation I've seen so far as to why the NSA's hoarding of metadata is truly as -- if not more -- concerning than if the government were surveilling the actual content of our phone or online communications.
Blaze explains that, given the scale of data collection, the government has amassed what could be called "a National Relationship Database." He writes:
Metadata is our context. And that can reveal far more about us — both individually and as groups — than the words we speak.
Context yields insights into who we are and the implicit, hidden relationships between us. A complete set of all the calling records for an entire country is therefore a record not just of how the phone is used, but, coupled with powerful software, of our importance to each other, our interests, values, and the various roles we play.
The better understood the patterns of a particular group’s behavior, the more useful it is. This makes using metadata to identify lone-wolf Al Qaeda sympathizers (a tiny minority about whose social behavior relatively little is known) a lot harder than, say, rooting out Tea Partiers or Wall Street Occupiers, let alone the people with whom we share our beds.
It is, in effect, a National Relationship Database.
Blaze stresses too that what's important about a mass collection of metadata is that -- being network- and relationship-based as it is -- opting out of these mechanisms of surveillance as an individual, or even a small group, is very difficult indeed:
Individually, there’s not much we can do to opt out. As a technologist, my instinct is to use technology to counter technology. It’s not so easy. Content can be protected, somewhat inconveniently yet effectively enough, with encryption. But we leave trails of metadata everywhere, anytime we reach out to another person. And while there are techniques (such as Tor) that can defeat metadata traffic analysis under some circumstances, they don’t cover all the ways we communicate.