Why does one need a high level of privacy/anonymity for legal activities?
One real world example - when you are naked in your shower, not doing anything wrong, would you like it if everyone came by and took pictures? Or televised your shower for the world? Probably not.
Another example - if I send a love letter, or write a will dividing up my savings, should that be published on the front page of the national papers? Again - no.
If I am carrying out my own business, the expectation should be that I have privacy, except where I have consciously and deliberately waived it. This was the case before technology became pervasive - it should still be the case. In the old days law enforcement needed a warrant before they could access your property or communications, because the assumption has to be innocent until proven guilty. This has been eroded as technology has developed.
If I encrypt all my emails to my friends, the expectation should not be that I am a criminal for doing it, just that I want privacy, like leaving a room to take a private phone call. I could be planning a surprise birthday party, or applying for a new job, or possibly just enjoy using PGP - it doesn't really matter - it's my business.
From the EFF's privacy page:
Privacy rights are enshrined in our Constitution for a reason — a thriving democracy requires respect for individuals' autonomy as well as anonymous speech and association. These rights must be balanced against legitimate concerns like law enforcement, but checks must be put in place to prevent abuse of government powers.
Admittedly, I don't live in the US, but those constitutional rights sound good to me.
There are a great many tweets, blog posts, articles, papers and books on this topic. Here are summaries of three of them in order of accessibility. First some quips in response to the classic question (from Schneier, see below for why these aren't the right answer though).
- "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."
And a recent quip from Snowden:
- "Arguing that you don't care about the right to privacy because you have nothing to hide is no different than saying you don't care about free speech because you have nothing to say."
Falkvinge has a good brief blog post on this topic, further summarised here:
The rules might change. Do you know what the next government's policies and laws are going to be? You know, the government voted in by that relatively small voting group that you fundamentally disagree with but managed to form part of a coalition government?
It's not you who decide if you have something to fear. It's automated surveillance software. People will start to behave not just based on what is legal or right, but based on a desire to avoid being flagged.
Laws must be broken for society to progress. A controversial statement when you first come across it, but self-evident when you think about it (the legality of homosexuality is a good example). Lack of privacy prevents this.
Privacy is a basic human need. See @Andrew and @Rory's answers for some obvious examples, and the paper below for a deeper understanding.
Schneier, predictably, has a (short) essay on this topic. He argues (like Solove - see below - but more accessible) that the question is wrong to frame privacy about hiding wrongs. He prefers to frame the debate as liberty vs tyranny.
On abuse of data:
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.
If you're looking for more in depth treatment, try Daniel Solove's paper, who argues that there is a fundamental problem with the focus of the question on privacy as just being about hiding. Here's an online version of the arguments from the same author.
On this topic:
The harms consist of those created by bureaucracies—indifference, errors, abuses, frustration, and lack of transparency and accountability.
On why privacy should be a default for information, not just on information you consider to be directly sensitive:
Aggregation, however, means that by combining pieces of information we might not care to conceal, the government can glean information about us that we might really want to conceal.
The problems of surveillance by a government in particular
it creates a power imbalance between individuals and the government ... This issue is not about whether the information gathered is something people want to hide, but rather about the power and the structure of government.
One of the problems found in countering this argument is that it doesn't sell very well:
At the end of the day, privacy is not a horror movie, and demanding more palpable harms [caused by privacy violations] will be difficult in many cases. Yet there is still a harm worth addressing, even if it is not sensationalistic.
So, the one liners at the top of this answer are weak responses, as in responding in that manner you've already fallen into the trap of focussing solely on the aspect of privacy that is about hiding wrongs or embarrassing information.
You may also want to check out Lessons From The Identity Trail, a book formed from a fantastic collection of papers, now freely available, that were the output from a multimillion dollar study on privacy, identity and anonymity.
Turn the question around
We would need a society where everyone was trustworthy.
- All ISP's that handle my traffic.
- All Web sites.
- All users on the Internet, for every country.
- All governments (how many wars right now).
- All companies.
- All staff of every company.
- All aliens (they are out there).
If we don't encrypt communication and lock systems then it would be like:
- Sending letters with transparent envelopes.
- Living with transparent clothes, buildings and cars.
- Having a webcam for your bed and in your bathroom.
- Leaving unlocked cars, homes and bikes.
All of this makes it clear that there is no way that we should give up all security technologies just because you trust your ISP or Government, you must trust EVERONE IN THE WORLD to make a 'drop your pants' strategy viable.