Facebook has added a new feature called “Facebook Groups” which allows your friends to add you to groups they create.
The only problem with the feature is that you cannot opt out of it. For a real life example, NAMBLA, the pedophilia association created a group and then proceeded to add people to it, and when users logged on, they saw updates that said they joined NAMBLA, when in fact someone added them without their permission.
The Facebook Help Center answers the question “Can I Prevent People From Adding Me to a New Group?” with the following: “The functionality of approving a group membership is not available. Similar to being tagged in a photo, you can only be added to a group by one of your friends. When a friend adds you to a group, a story in the group (and in News Feed for Open or Closed groups) will indicate that your friend has added you to a group.”