Was the Man in the Black the first-and-only Smoke Monster ever to inhabit the Island? It's at least debatable. I don't think Mother was one. If there were others, we never met them, except perhaps in that Egyptian hieroglyph Ben found beneath the Temple. I put these possibilities together in the suggestion that there's a potential Smoke Monster inside all of us. That mankind has been dealing with the worst of himself from the inside out, the death and the black stuff, since the beginning of time. And there's a real danger in unleashing that darkness and deception on the world. Still, it's not him leaving the Island that would spell doom for mankind. As we've said before, there is enough evil back in the world to do just fine at bringing about our own end, thank you. It's the conditions that would need to exist that would allow him to leave that would spell the end.
And what were those conditions? Pulling the plug turned out the Light. I understood the light as a metaphor for a combination of free will and original sin. The light of humanity. The choice that makes us different from the animals. The gleam that allows us to do good but also pre-ordains us to sinfulness and selfishness. What I did not expect was for water to stop flowing into the cavern when the plug was pulled. This was a big clue for me, and it finally answered a very big but extremely subtle question the show had presented to us this season: what was with all the water? Characters continually filling up bottles or canteens. Drinking water at odd times. Downing it as the act of faith that transforms one into an Island protector. It was the textbook case of "Water, water everywhere." Biblically, of course, we know of the concept of "living water" that quenches thirst for good, and comes pouring out of those who know Christ. Empirically, water (and light) are the ingredients of life that scientists look for throughout the universe to see if we are alone or not. The concepts work for all views. What is important is that there is a flow. Input, output. Life keeps moving, water keeps moving, time keeps moving. Dry it up, and there is nothingness. Barrenness.
This is why, I think, the Island is shown at the bottom of the ocean in what we are calling DeadWorld. Life has stopped there. You enter with the spark having gone out. But that is also why it is crucial for the living not to let the Island sink into the sea. If you do that, all you have is the DeadWorld. And if that is all you have, then there is no playing field, no gameboard, no proving ground, no test facility that is this life. No preparation. No chances. No redemption. No beginnings.
Jack Shephard passed his test, as did several other characters. It was never easy for him, as Locke once told him. Embracing the faith journey is next to impossible, but nothing is irreversible. Well, except Death. Although even in death you can receive second chances to work through things. But what about those who are dead on the Island? Those - like Michael, apparently - who are stuck in something very much like purgatory, who don't get to enter second-chance DeadWorld, but neither do they appear trapped under the Island in the lake of sulfur? I can only guess that Michael and the other whisperers are there because the Island, with its close proximity to "hell," serves as their own prison. They aren't worthy of being "in" Hell, but they are doomed to walk "on" it. Or maybe because the Island does have such close ties to Death and inescapability, those who die on or near the Island are stuck there. For the record, though, I don't see how that can be the case, as Boone, Shannon, and Jack and others are able to exist in DeadWorld as well as move on to "Heaven."