From now on I will write theories on Locke only...lol
I believe Locke is not MIB. It is my belief. You can agree or disagree with me. It will probably be the second one. I base my evidence on show and the conversation I heard. Conversation between Jacob and MIB at the beginning of the Incident.
MIB: Do you have any idea how badly I wanna kill you?
JACOB: Yes.
MIB: One of these days, sooner or later... I'm going to find a loophole, my friend.
JACOB: Well, when you do, I'll be right here.
Let me repeat the last thing MIB said.
JACOB: Well, when you do, I'LL BE RIGHT HERE.
But when the BIG DAY came MIB (Locke) had no idea where to find Jacob.. ?
If he pretended...hm I don't see the logic in that since we already saw he knew were Temple was, he knew how and where to find Smoke Monster, Richard noticed that Locke has changed..etc. Then why would he pretend? It would be just another point for him among his people. He is the leader now, right.
This sentence is somewhere in the back of my head.
I need you to find purpose.
And I think it was Christian (Smoke Monster) who told him that.
Later on when we see Locke changed, he said: I have a purpose now.
So, would it be so hard to think that there is a third option..third solution to what is happening to Locke now.
I know that at the end of the Incident Jacob told him "I see you found your loophole" implying that this man in front of him is MiB from the beginning of the episode but it doesn't mean anything. It can be a misdirection and it wouldn't be the first time. Who knows how many times Locke had conversation with Jacob that we are not aware of. Or it could be just a stage for Ben.
I mean nothing here is black and white, nor gray.
He cannot be the Smoke Monster either. Because Smoke Monster uses bodies. And whenever that happens the body disappears.
Christian Disappeared from the coffin.
Yemi disappeared from the plane.
Lockes body duplicated. It didn't disappear. It DUPLICATED.
The other thing. Smoke monster lives on the BIG island, main island. And it is a security system for that island. It doesn't go near water..and until we are told there are tunnels connecting Hydra and the main island I will think there is no way that Smoke swam across in order to posses Locke. Another thing, at the time Sun and Frank were talking to Christian, confirmed Smoke Monster, Locke was talking to Ilana and Jacobs gang. So it doesn't really matter that once Locke was out of the picture Smoke would come or other way around.
I also wonder if Illana and Bram knew from the start that there are two Lockes, why would she leave him out her sight? If he is dangerous and a threat to Jacob? I seriously doubt they found his body a wee bit later..because Locke was around at least 2 days before he took off with Ben. He stayed by his bed the whole time, remember?
For the end, Smoke Monster is the security system for the island. It PROTECTS the island. And as Far as I know it was Smoke Monster who appeared as Alex (who was by the way unburied by Miles and Sawyer) threatening to kill Ben if he as much as put his finger on Locke. So it seems to me Smoke Monster PROTECTS Locke too.
So many times Locke said: The island told me.
At the time he had no idea what he is talking. Because it was he himself who told him what to do.
The island told him Boone will die. (it was Locke seeing his future and bloody Boone who told him in the future about Theresa)
The island told him to find the Nigerian plane. (but it was locke who will in his future and islands past see the plane getting down and where)
The island told him Eko will die, and his death will be caused by Yemi somehow and that Eko will fall from a height (it was Locke who saw Smoke Monster killing Eko)
So all these things island told him, it was in fact Locke seeing future, future he will participate, through dreams.
So far Locke is his own cause.
Let me just repeat this for the end.
Smoke Monster is a security system.
Smoke Monster PROTECTS THE ISLAND.
Smoke Monster PROTECTS LOCKE.