You think your world is safe, it is an illusion; a comforting lie told to protect you.
Obviously not in the movie itself, these lines tell us why the attack happened. Because Vulcan was like an attack on Britain, hit hard but it wasn't a hit at home. San Fransisco was the hit at home. Just as 9/11 was, the attack was the end of our security. It goes to prove that even the most powerful military on Earth (or in the galaxy) could not put a stop to a madman, and many lives were lost. 9/11 was more than an attack, it was a blow to our thoughts of safety. It was an attack on our peace of mind where people were convinced that it wouldn't happen here, but it did.
It could never happen on Earth, much less Starfleet Headquarters, but it did.