Over the years Facebook has grown and they have slowly been gathering information on everyone. Things that used to be private are now public. These are not being communicated to people as it happens. As well it is overly complicated to keep up on the privacy settings as they change frequently.
See this image that shows you what information is now PUBLIC and being sold to 3rd party companies
Click the picture below to view in a larger format.
Check this website to find out how to delete your facebook account
http://www.wikihow.com/Permanently-Delete-a-Facebook-Account