You can't fully leave Facebook. People can still tag you on photos they take even when you don't have an account. (Just a text tag, but it could still be incriminating...)
But this is true even if you never had an account. That's like saying you can't leave the internet, because people can still talk about you online.
True. But I guess as a social utility the internet and facebook are more evasive than people assume. I think, facebook more so, because if you know anybody that uses it, you lose more 'privacy'.