At least people should know that before using it...not everyone has many secrets to hide. What's the point hiding who you make friends with, and public conversations? Trying too hard to stay off the grid is rather creepy...
Do you see the value of the information for the illegitimate regime to use?
Mapping someones friends by good old detective work is not that difficult. It just takes time. It will also reveal much more than your facebook account will. What is frightening to me is the automation. It simplifies your relations to people and can lead to some unpleasant connections.
People should also be educated about the fact that facebook is not a private forum. Everyone knows not to bitch about their boss too loudly in the cafeteria. But for some reason they are happy to write about it to their wall.
A Facebook profile is better in someways than a thumb print or DNA. Net-citizens can be automatically character profiled.
You also don't need everyone to use the system to grasp a people's mindset.