Don't be so quick to blame the end user. It's not always obvious when you're adding personal information to facebook.
Case in point: Using the facebook app on an iPhone (unsure about other smart phones) automatically adds your phone number to your personal details. And woe unto those who use "Contact sync", facebook will not only update your personal details with your phone number. It will also take all the phone numbers of your friends and family and upload those
Blogspam with details
You can see this for yourself. Go to: Account -> Edit friends -> Phonebook.
There was a minor furor when this first came out and everyone appears to have forgotten it.