[roc]

One quibble: Metadata is facts about people. Logging meta-data isn't a slippery-slope toward also catching facts. It's a problem from the jump.

"Joe goes to the gym three times a week" is a fact.

"Joe's network activity originates from a gym on the following schedule" is not only at least an equivalent fact, in practice it's far superior to the simple case. It can give you subtleties [1], it's less susceptible to subterfuge [2], it gives you actionable evidence of specific occurrences, etc.

Consider the CIA doesn't use meta-data to target hellfire missiles because it's less identifying than actual data. They use it because it's far better.

[1] Joe never goes to the gym on Saturday. Joe goes to the gym more during the spring than the winter. Joe almost never misses a day when Sally is at the gym. Joe and Sally nearly always leave at the same time.

[2] It's trivial for someone to say they go to the gym on a schedule they don't. It's not even too difficult to get a second or third party to fudge, embellish or outright lie on their behalf. It's much more difficult to get a second or third party to help you make your device convincingly take the claimed routine, without you creating any conflicting meta-data that gives up the ruse.

[TeMPOraL]

This is important and should be a top-level post. I think many people miss this in discussions about privacy, and this is the reason I believe the privacy is dead. Everything you do is metadata about everything else you do, about everything else people around you do. You can infer any piece of "data" you want given enough (meta)data sources and computing power.

Thus the only way we can keep privacy would be to roll back the last 50 years of technological progress, and that's why I'm starting to entertain a thought that we (as a society) should drop the concept entirely and tackle the change head-on, instead of being dragged there by force by the ongoing progress of technology.