The most common retort against privacy advocates – by those in favor of ID checks, cameras, databases, data mining and other wholesale surveillance measures – is this line: "If you aren't doing anything wrong, what do you have to hide?"

Some clever answers: "If I'm not doing anything wrong, then you have no cause to watch me." "Because the government gets to define what's wrong, and they keep changing the definition." "Because you might do something wrong with my information." My problem with quips like these – as right as they are – is that they accept the premise that privacy is about hiding a wrong. It's not. Privacy is an inherent human right, and a requirement for maintaining the human condition with dignity and respect.

Two proverbs say it best: Quis custodiet custodes ipsos? ("Who watches the watchers?") and "Absolute power corrupts absolutely."

Cardinal Richelieu understood the value of surveillance when he famously said, "If one would give me six lines written by the hand of the most honest man, I would find something in them to have him hanged." Watch someone long enough, and you'll find something to arrest – or just blackmail – with. Privacy is important because without it, surveillance information will be abused: to peep, to sell to marketers and to spy on political enemies – whoever they happen to be at the time.

Privacy protects us from abuses by those in power, even if we're doing nothing wrong at the time of surveillance.

We do nothing wrong when we make love or go to the bathroom. We are not deliberately hiding anything when we seek out private places for reflection or conversation. We keep private journals, sing in the privacy of the shower, and write letters to secret lovers and then burn them. Privacy is a basic human need.

A future in which privacy would face constant assault was so alien to the framers of the Constitution that it never occurred to them to call out privacy as an explicit right. Privacy was inherent to the nobility of their being and their cause. Of course being watched in your own home was unreasonable. Watching at all was an act so unseemly as to be inconceivable among gentlemen in their day. You watched convicted criminals, not free citizens. You ruled your own home. It's intrinsic to the concept of liberty.

For if we are observed in all matters, we are constantly under threat of correction, judgment, criticism, even plagiarism of our own uniqueness. We become children, fettered under watchful eyes, constantly fearful that – either now or in the uncertain future – patterns we leave behind will be brought back to implicate us, by whatever authority has now become focused upon our once-private and innocent acts. We lose our individuality, because everything we do is observable and recordable.

How many of us have paused during conversation in the past four-and-a-half years, suddenly aware that we might be eavesdropped on? Probably it was a phone conversation, although maybe it was an e-mail or instant-message exchange or a conversation in a public place. Maybe the topic was terrorism, or politics, or Islam. We stop suddenly, momentarily afraid that our words might be taken out of context, then we laugh at our paranoia and go on. But our demeanor has changed, and our words are subtly altered.

This is the loss of freedom we face when our privacy is taken from us. This is life in former East Germany, or life in Saddam Hussein's Iraq. And it's our future as we allow an ever-intrusive eye into our personal, private lives.

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.

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Bruce Schneier is the CTO of Counterpane Internet Security and the author of Beyond Fear: Thinking Sensibly About Security in an Uncertain World. You can contact him through his website.