Uploaded willfully by the people concerned. What is hard to understand about "don't put something online you don't want others to have access to"? (Values of "others" change with the service involved.. but you'd have to be frankly, moronic to put something on a social network site and not expect it to be accessible to others, as well as authorities if they come knocking)
However, I was thinking more about private messages and chats, tracking cookies, etc. Also pernicious: being tagged in other people's content.
Tying a real name to private data can have repercussions, even for responsible law abiding adults -- especially when the data is archived indefinitely, in one convenient central location.
On top of that you are putting the responsibility on people to "think of every bad use of this information which could happen, and if you are still happy, then post it". Which is an impossible task. Much better to enumerate what can happen, what it will be used for, which can be made a limited set of things, and then if you are happy with that, post it.
Does Mark Zuckerburg strike you as the kind of fella who will go to prison to fight for your privacy?