Nothing is irreversible by Kazao

I have had this theory for quite a while and if it has been said then I'm sorry.
Part 1
Okay I think somewhere in the temple is the gateway to another dimension. I believe that when Ben was shot and they brought him there he wasn't healed. I think he was swapped for another version of himself. Richard said that he wouldn't know what happened to him and he would never be the same, that's why he doesn't remember because the real Ben died and he was replaced by another version of him.

Part 2
Jacob is not from this dimension but from another one. I think he was part of another group of 'others' in an alternate reality. I think he had a group of friends who passed away so he chose to bring them back. The first friend was the man in black. But like Richard said there was a personality change. MIB was not the same friend and Jacob was disappointed by that. In the episode the Incident MIB revealed he wanted to kill Jacob. But Jacob hardly reacted to that. It seems that he cares about his friend too much to cause him harm.

Part 3
I said in part 2 that Jacob had a group that died. I think he learned his lesson from the MIB that he shouldn't bring people from other places, so he did not bring his friends. So instead he too the MIB and they both traveled through to an alternate reality. Instead of bringing his friends to him he chose to go to them. Those friends that died in this reality are Jack, Kate, Sawyer, Hurley, and Sayid. (possibly john locke because he was touched by jacob as well) But Jacob went through a personality change as well. He was manipulating, using lists and controlling the others to get what he wanted. He talks about free will but he has been using his abilities to bring his friends to the island. This also fits in with what the MIB said. When he said he wanted to go "home" he meant to his original dimension the one where Jacob took him from. I think the two sides of this isn't good vs evil, but Jacob wanting to recreate his 'family' and the MIB just wanting to leave.