So Jacob claims that the island is preventing evil from spilling over, like a cork keeps the wine in a bottle. The implication is that MIB is evil and that Jacob wants to help keep him contained. However Jacob is also bringing people to the island in order to "prove his point." Doesn't Jacob realize that by doing so he creates the possibility that MIB will get one of these people (since he can't do it himself) to kill him, and then escape. If your goal was really to keep evil contained to the island, wouldn't you avoid doing anything that would allow you to fail? It might be possible that Jacob is figuring out a way to kill MIB, but he doesn't need to. As long as MIB is on the island, everyone else is safe. So there's no real point in bringing anyone else there. Just let MIB and the island be and quit bringing others there.
This has me thinking about what's going. Either Jacob is lying about MIB being the evil force needing to be containe, or Jacob is a total dumb@$$.
If he's not lying, better hope they find out who the candidate is real soon. Or else evil MIB is going to escape, and it's all douchebag Jacob's fault.