Well there is really nothing to enforce when you agree to Facebooks TOS and Privacy Policy upon signing up. Facebook has never forced you to sign up.

Excerpt from privacy policy: Certain categories of information such as your name, profile photo, list of friends and pages you are a fan of, gender, geographic region, and networks you belong to are considered publicly available, and therefore do not have privacy settings. You can limit the ability of others to find this information on third party search engines through your search privacy settings.