So if the island has a protector, he has to stay. But if there is no protector he is free to leave? So he has to make sure that one way or another, none of Jacob's chosen ones takes on the job....which is why Richard told Sawyer he will try to kill everyone. ahhh...
So when he says the island doesn't need protecting from anyone and "the island" will be perfectly fine, protector or no, is it more a case that Jacob was a jailor - keeping Fake Locke (does that guy have a name anyway, the guy who took John's form?) imprisoned - in order to protect the rest of the world from him perhaps. Hmmmm....