Because you can’t opt out. Facebook creates shadow profiles for people who have never created an account. They track people’s faces in photos they appear in that were posted by friends. They link people’s personal information to their shadow profile whenever a user allows Facebook to access their address book contacts.
Facebook is a pervasive, all-consuming data monster. If lawmakers don’t rein it in, it will grow so powerful that it will challenge the sovereignty of governments. It’s not a joke.