Imagine the (legitimate) outcry if a local municipality, a State government, or the Federal government in the US deployed an infrastructure that would systematically identify and track people as they went about their daily lives, without a viable option to opt out. While the US has laws that govern when and how data about individuals could be used, the mere availability of such data would lead to temptations that would be irresistible in practice, yet not necessary for the functioning of this society.
Now imagine that this data is being collected for private use by a company that then uses it for whatever purpose it wants, including giving it up to the government without a warrant. Not the kind of deal anyone would want to sign up for, I assume.
Now stop imagining, because this is happening now: Google, for example, is collecting location data from Android devices and using it against its mapped databases of malls and other public places. Given Google’s record on privacy with books, and email it seems unlikely that it will resist attempts by the government to turn over sensitive data, data that the government would not have had without Google having aggregated it in the first place.
Once the data are aggregated, there is no going back, no easy practical means to prevent it from being used for arbitrary purposes by anyone who can get their hands on it, whether it is our government, or someone else’s.
Today Google is selling your location to advertisers so that they can assault you with ads as you walk by a store. But that same data, properly mined, can be used to surveil you for kidnapping, for example. Seems far-fetch now, perhaps, unless you live in Mexico.
The best way to prevent this kind of information from being used is to prevent it from being collected in the first place.