User blog comment:Zero15/Code Geass R3/@comment-9186322-20130506232011/@comment-99.238.130.205-20130507223735

The part about C.C. saying her wish can be fulfilled is answered quite explicitly in the anime. Only those with the strongest level of Geass can remove the Code (code for immortality) from C.C. and kill her.

Lelouch didn't grant his geass to the world. He took control of it, and told the world to continue to advance. He isn't a saint, nor is he meant to be. He's supposed to be badass beyond recognition.