In the twentieth century world most of us were born into, there was an assumption of privacy through anonymity simply because it was hard to keep track of everyone. Unless you were a wanted felon, moving to a new town essentially meant a new start in life. But with the amount of information that's collected and processed today, that simply isn't the case. Even if you keep a low profile on social media, you're still going to be tracked by a banks, credit card companies, and a multitude of private corporations and government agencies.
We can make laws against the buying and selling of personal information, but these are going to be hard to enforce. For example, a small retail chain might build up a private database of their customers. What happens if this chain is simply bought by a larger company? Can this company hold onto the customer database or are they forced to destroy this information? What if they split the company into retail and wholesale operations?
To be fair, saying that laws are hard isn't a reason not to make laws, it's just that we should have a clear understanding of how difficult it's going to be to maintain privacy in an era of cheap cameras, facial recognition software and ubiquitous computing. We can make it difficult for individuals to have access to this information, but it's going to be really hard to prevent deep pocketed organizations from collecting this information. The danger is that privacy laws will ensure that the public doesn't have access to information that large corporations and government agencies have access to.
We really need to consider what type of personal information is private and what ought to be understood as public. For example, if I own a house, is that information private or public? If you think that should be private, you have to make the argument that we're better off living in a society in which it's difficult for members of the public to find out who a piece of property belongs to. What about a car? If I inherit a million dollars, should I be able to keep that information private? What about who I marry or divorce, or who my children are?
Certainly there are some things that should be private. Encryption works, and we should be able to hold private conversations. One could make a strong case that medical records ought to be private. But we need to have a clear understanding of how we're going to keep these things private, and what are the costs and possible consequences of keeping things out of the public sphere.