if you have nothing to hide, you have nothing to fear

This is a very dangerous mindset. The argument is frequently raised in debates by pro-big brother hawks, and doing so is dangerous, cowardly, and dishonest.

There are at least four good reasons to reject this argument solidly and uncompromisingly: The rules may change, it's not you who determine if you're guilty, laws must be broken for society to progress, and privacy is a basic human need.

One – The rules may change:

Once the invasive surveillance is in place to enforce rules that you agree with, the ruleset that is being enforced could change in ways that you don’t agree with at all – but then, it is too late to protest the surveillance. For example, you may agree to cameras in every home to prevent domestic violence (“and domestic violence only”) – but the next day, a new political force in power could decide that homosexuality will again be illegal, and they will use the existing home cameras to enforce their new rules. Any surveillance must be regarded in terms of how it can be abused by a worse power than today’s.

Two – It’s not you who determine if you have something to fear:

You may consider yourself law-abidingly white as snow, and it won’t matter a bit. What does matter is whether you set off the red flags in the mostly-automated surveillance, where bureaucrats look at your life in microscopic detail through a long paper tube to search for patterns. When you stop your car at the main prostitution street for two hours every Friday night, the Social Services Authority will draw certain conclusions from that data point, and won’t care about the fact that you help your elderly grandmother – who lives there – with her weekly groceries. When you frequently stop at a certain bar on your way driving home from work, the Department of Driving Licenses will draw certain conclusions as to your eligibility for future driving licenses – regardless of the fact that you think they serve the world’s best reindeer meatballs in that bar, and never had had a single beer there. People will stop thinking in terms of what is legal, and start acting in self-censorship to avoid being red-flagged, out of pure self-preservation. (It doesn’t matter that somebody in the right might possibly and eventually be cleared – after having been investigated for six months, you will have lost both custody of your children, your job, and possibly your home.)

Three – Laws must be broken for society to progress:

A society which can enforce all of its laws will stop dead in its tracks. The mindset of “rounding up criminals is good for society” is a very dangerous one, for in hindsight, it may turn out that the criminals were the ones in the moral right. Less than a human lifetime ago, if you were born a homosexual, you were criminal from birth. If today’s surveillance level had existed in the 1950s and 60s, the lobby groups for sexual equality could never have formed; it would have been just a matter of rounding up the organized criminals (“and who could possibly object to fighting organized crime?”). If today’s surveillance level had existed in the 1950s and 60s, homosexuality would still be illegal and homosexual people would be criminals by birth. It is an absolute necessity to be able to break unjust laws for society to progress and question its own values, in order to learn from mistakes and move on as a society.

Four – Privacy is a basic human need:

Implying that only the dishonest people have need of any privacy ignores a basic property of the human psyche, and sends a creepy message of strong discomfort. We have a fundamental need for privacy. I lock the door when I go to the men’s room, despite the fact that nothing secret happens in there: I just want to keep that activity to myself, I have a fundamental need to do so, and any society must respect that fundamental need for privacy. In every society that doesn’t, citizens have responded with subterfuge and created their own private areas out of reach of the governmental surveillance, not because they are criminal, but because doing so is a fundamental human need.

Source: http://falkvinge.net/2012/07/19/debunking-the-dangerous-nothing-to-hide-nothing-to-fear/