Bruce Schneier is on the money in his recent Wired article "The Eternal Value of Privacy"
Privacy protects us from abuses by those in power, even if we're doing nothing wrong at the time of surveillance.
Too many wrongly characterize the debate as "security versus privacy." The real choice is liberty versus control. Tyranny, whether it arises under threat of foreign physical attack or under constant domestic authoritative scrutiny, is still tyranny. Liberty requires security without intrusion, security plus privacy. Widespread police surveillance is the very definition of a police state. And that's why we should champion privacy even when we have nothing to hide.