not my original theory, but definitely the one i have jumped on board with now....
the island serves as the gates to the lost city of atlantis....i.e. weird animals/4-toed monstrous statues....the gate opens every 108 minutes so pushing the button keeps the gate closed....by des using his key the sealed the gate "permanantly" with echo, locke, and des crossing over....the others know of the gate and are the "good guys" by keeping it a secret and keeping it safe...
