In a nutshell, the ethics of privacy can be derived from the fact that knowledge is power. The more people know about you, the more power they have over you.
Did someone say power? That's a big clue that the principle of symmetry should apply here. We can boil the question down to "Is symmetry between the sender and the receiver maintained?"
We can get a clue from the section describing the symmetry property. We can recast the privacy problem into an economic one, where "economic" is used broadly to mean not just monetary issues, but all value transfers a person may wish to engage in. One of the basic ethical principles of a free economy is that with few exceptions, people are allowed to set the value of what they own. When a person is not free to set the value of what they own, they are effectively under the power of the entity that is setting the "price" for the goods or service.
Examples of this are easy to see by turning to the government. It is illegal to sell body parts. It is illegal to sell yourself or anyone else into slavery. In most parts of the US, prostitution is illegal. None of these things are physically impossible now that there is a law; instead, the "price" for doing these things is significant jail time and/or stiff fines (if you're caught!). On the flip side, where a government can force lower prices, it is illegal to abuse a monopoly to artificially inflate prices. Many prices are subsidized by a government to keep the goods or services available to all, such as Canada's "free" health care. Illegal drug possession can carry stiff consequences. All of these demonstrate how power can be exerted simply by increasing and decreasing the perceived values of various actions and objects.
("Free" gets scare-quoted because I prefer the more accurate term "paid for". Try replacing "paid for" wherever you see the word "free" in advertising; usually the advertisement is much less appealing after that.)
Generally, we want to reserve this unilateral power to governments. A relationship between two persons or person-like entities should be governed by mutual agreement, which is really another expression of the symmetry property: There is nothing special about either entity in such a relationship that entitles one or the other to special privileges. (Ideally, the government is By The People, For The People anyhow so even the powers reserved to the government are in some sense consensual, although in a collective sense rather then an individual sense.)
Using this analysis, we can construct a more active and practically useful definition of privacy:
- Privacy
- Privacy is violated when information of some value is taken from entity A by entity B and used in some manner that might cause A some form of non-monetary harm, without B compensating A in some mutually agreeable manner.
You could cast this in purely economic terms by dropping the phrase "and used in some manner that might cause A some form of non-monetary harm" without too much loss, but that allows too many cases that are purely economic, which I think fails to capture the sense of what people mean by privacy. If I steal a valuable product design document from you and sell it on eBay, that would fit a purely economic definition of privacy as it may cause great monetary harm, but most people would consider that just theft, not a privacy issue. So let us confine ourselves to discussing non-monetary harm, which as I mentioned above ranges from "minor annoyance" to "life-threatening". I also observe that this is not always a strict separation; one privacy violation can cause both monetary and non-monetary forms of harm at the same time, possibly constituting both theft and a privacy violation.
This definition has a distinct advantage over the previous one: It provides us with an easy yardstick to examine privacy relationships in the world around us to determine how ethical they are. We can also define privacy-sensitive information:
- privacy-sensitive information
- Information that could cause an entity non-economic harm, which the entity may or may not be willing to sell for some price.
You could probably write this next section now without me spelling it out for you, but good essay form requires me to do it anyhow, so please bear with me as we apply the yardstick to real life.