If you only trust 6 people to have access to your email address then customise Facebook's privacy settings to only let those people see it. You don't have to trade data security for access to friends.
Facebook can't protect you from every way your friends could mishandle the data you give them access to. If you don't want them to have access to part of your profile it's up to you to set your privacy permissions appropriately, and it's Facebook's responsibility to make that as easy as possible (which they haven't).
Facebook can't protect you from every way your friends could mishandle the data you give them access to. If you don't want them to have access to part of your profile it's up to you to set your privacy permissions appropriately, and it's Facebook's responsibility to make that as easy as possible (which they haven't).