Locke was also 'Claimed' by Gravastars

'What kate does' gave us a vital clue as to the nature of the monster's influence, and the healing effects of the island.

What we've seen so far-

-The 'sickness' or 'infection' of the monster seems to spread or perpetuate as the body heals itself from injury. So far we've seen this with Claire (house explosion), Montand (arm ripping off), Young Ben (recovering from a gunshot wound), and Sayid (actually waking from the dead).
-In each case, the person healed seems to grow 'darker' or more corrupt in a way.

I believe both the 'darkness' and the 'healing' are caused by the assimilation of the monster within the afflicted - disrupting and influencing their brain and limb functions. For a more psuedo-scientific explanation, the monster can stealthily enter a person's wounds to heal them, and at the same time can use its obvious electronic nature (see those sparks coursing through it?) to take complete control of certain neurons or muscles.

This is why Ben is morally unhinged, and why Claire would leave her baby to walk off with 'Christian'.

These traits at one point, could also be attributed to a pre-dead Locke. Remember back in the season 3 finale? 'Walt' visits Locke in what seems to be his premature grave, and what happens next can only be described as a miracle. Locke is healed. He is alive. He can even walk again.

Now think back to Locke's actions in season 4. He is almost completely power-ruthless and corrupt; at one point sticking a grenade in Miles's mouth and remorselessly throwing a knife into Naomi's back. At this point, Locke was also 'Claimed' - all the monster needed then was to get Locke off the island. And the rest is history.

So what is the meaning of it all? I believe the monster's 'claiming' differs from its usual disguises (Flocke, Fake yemi) insofar that it can directly manipulate a person's fated path, and guide them to do terrible things (Fight, destroy, corrupt). If we want to really stretch this theory, who is to say that Michael wasn't also 'claimed' when he shot Ana Lucia and Libby?