Via the Chronicle of Higher Education, law professor Daniel J. Solove reveals all:
The nothing-to-hide argument is everywhere. In Britain, for example, the government has installed millions of public-surveillance cameras in cities and towns, which are watched by officials via closed-circuit television. In a campaign slogan for the program, the government declares: “If you’ve got nothing to hide, you’ve got nothing to fear.”
But the problem with the nothing-to-hide argument is the underlying assumption that privacy is about hiding bad things. By accepting this assumption, we concede far too much ground and invite an unproductive discussion about information that people would very likely want to hide. As the computer-security specialist Schneier aptly notes, the nothing-to-hide argument stems from a faulty “premise that privacy is about hiding a wrong.” Surveillance, for example, can inhibit such lawful activities as free speech, free association, and other First Amendment rights essential for democracy.
One such harm, for example, which I call aggregation, emerges from the fusion of small bits of seemingly innocuous data.