The island seems to have this kinky thing for taking innocence. There is the unresolved question as to why the others took some of the people from flight 815 to be with them and not the ‘less innocent ones’. It was implied that those taken were told to be taken (presumably by Ben or the island) because they were innocent. I offer the idea that the island needed their innocence.
It seems to harvest innocence like one would eat food. It takes children and rears them in it’s own group of people controlled by Jacob (who seems to be a manifestation of the island, person or not as well) perhaps using their innocence; People seem to die when they ‘redeem’ themselves, restoring innocence; and of course it seems to be able to do things in return for innocence (like saving Ben). Maybe innocence is some sort of power source on the island that allows it to do it’s incredible things.
This idea was originally introduced by Locke with the death of Boone who he described as a sacrifice. Before Boone died Locke lost the ability to walk which had been granted to him by the island. Once the island had Boone’s innocence through his death it was able to help Locke again. In order to cure Ben injury which Juliet described as ‘incurable’ towards the end it needed to take every shred of innocence left in him. Just a theory I’m tossing out there. Any thoughts?