A lot of speculation has led theorists to question whether or not Charles Widmore is actually a part of this "game,"and is on either Jacob or MiB's side, or if he is a third party, with a different intention.
Since Widmore has been introduced, we have been, for lack of a better word, preached to about his evilness by Benjamin Linus. Although Ben feels that he, himself, is not special, and that he was lied to by Jacob and his own heart (both of which told him he had a special aspect to him, and meaning to his life), he is special. Special enough to speak Richard, and therefore special enough to probably have been told by Richard (who is, at the time, the Others' only link to Jacob) that Widmore is not a good man, and any effort by him to outcome come to the island must be thwarted.
We know now that MiB has been trying to get off of the island since he was introduced, and that Jacob needs to (or, now that we know about the "cork", chooses to) stay to keep him on it. In addition, we've learned that since Widmore has been introduced, Ben has told us that he wants to come to the island, for nothing more than using it for his own profit and benefit.
We've also learned that Jacob has candidates, which he has chosen to potentially take his place. Clearly if he's looking for candidates to replace him, he must be aware of his own death. Because we do have evidence that specific characters are aware of what's to come, other people might be aware that eventually, Jacob dies, and will need a replacement.
We know that the Dharma Initiative's goal at the Swan sight, was to study the electromagnetism. Why, then, were there so many stations which performed clear, psychologically altering effects on their inhabitants? Why did the Pearl Station only receive data, but wasn't able to transmit it back? Why did the Button absolutely need to be pushed? Why keep Desmond under the radar for so long, with such uncertainty of whether or not there is actually a purpose? Clearly, one could choose not to push the button, but that thought might linger in a person's head . . what COULD happen if I don't push it, maybe it's real!
After this thinking, what if the Dharma's purpose was not just to study the unique properties of the island, but to also to find a replacement for Jacob, to use for their own profit so they can be in control of the Island? Think about it, the fail-safe (get it, if you fail, this will keep you safe) key was there, so the Dharma Initiative must have been aware of at least some of the rules/abilities of the electromagnetism, and how it may prevent catastrophe if flipped (in spite of the lack of information the Dharma Initiative actually told it's workers/members, which made them seem unaware of the properties of the island's energy).
Desmond has a significant role to play in the outcome of this game. Is Jacob trying to prove to MiB that a human has the potential to take his place? Does someone have to use their free will to choose to take his place? Maybe he always dies, in every outcome of the loop (it always ends the same), and every time, there's a person who comes along, and among of those chosen by Jacob (touched), they take his place and prevent MiB from leaving the island. Everything until that person comes is just progress.
But what if it's a different candidate every time? Would it really matter, when they had no choice because to replace Jacob because they were touched, anyway, and would never be able to leave the island? What if there was a man, who, because of his special ability, could choose NOT to replace Jacob if the responsibility was laid on him? For example, if he chose to learn about a women, and even if he was told it was a direct violation of the rules, was able to find her.
I think that the preparation he experience in the Dharma Initiative, saving the world but sacrificing a normal life, and freedom, may have prepared Desmond to be the replacement for Jacob. His ability can allow him to decline the position, but because he isn't a candidate, Jacob will prove the MiB wrong: that a human can freely choose to sacrifice their life for the greater good. Desmond was not touched, and on top of that, he was exposed to a substantial amount of electromagnetivity, so he has undisputed choice in his existence, there is no rulebook for him. Perhaps every time a human has been given the power of this choice (like Desmond, who, maybe every single loop around has to make this same choice, has never been able to leave his son/Penny, and therefore the MiB always wins). if he were to choose to stay on the island for the rest of his life, and sacrifice his soulmate and son for the greater good of the world, MiB would have finally lost. The winner of this "gam! e" will come down to the offering of Jacob's position to the surviving candidate, and in every outcome (the way it always ends) they always choose to give into MiB's temptation, but this time, Desmond will sacrifice his life because he had already done it with the button, and he believes he is there now to serve a purpose.
Widmore is on the island to use Desmond to take Jacob's place, but Desmond has to choose for himself to disobey, and use it for the greater good (and be, ultimately, on Jacob's side). Desmond isn't special, like most theorists hypothesize, for the elimination of MiB; he's there for the safekeeping of the island, and to replace Jacob. Widmore wants to exploit its power, by manipulating Desmond to believe he's doing what he's doing for the greater good.