I have read a lot of blogs on the site about the nature of MiB and Jacob. The one prevailing assumption is that the characters must be either, good, evil, or gray. But gray is not the middle of good and evil, it is the middle of black and white.
Good and Evil are just abstractions of the human mind. How do you even define good? One could say that murder is ALWAYS evil, and one could say that it COULD be good. And being abstractions, they can't possibly have a middle ground, or "gray area", as they have no real definition or perameters. They are mere labels that we put on things, actions, and people; the result of a mental construction that we use to separate safety and danger, interest and disinterest, friends and enemies, pleasure and pain, etc.
This being said, I would stop thinking about whether or not Jacob is inherently good, as that depends entirely on other characters' points of interest, and begin accepting him as what he really is: a force or embodiment of a force opposite and equalized with the force embodied by MiB. We can clearly see that this is what they are by the heavy black and white symbolism associated with them. And to call either one "gray" would be to contradict the fact that the producers have worked hard to show us that they are NOT gray. There is no "gray" going on. The balance forged between the two forces is the EQUALIZATION between black and white, not the MINGLING of them. They are polarized forces.
It is not 2 + 2 + 2 + 2, it is 2 + 2 = 2 + 2.
What I'm trying to say is that in theories concerning the natures of the Jacob and MiB, the words Good, Evil, and Gray should never be considered. Though the two characters may once have been human, the balance between them is not a human (obviously), and therefore the polarized forces that they embody should not be associated with constructs of a human mind. Only the REACTIONS (by human characters) to this balance may be considered this way.
Now, this is also part of a story, and as we all know stories have heroes and villains. MiB is clearly represented as a villain, and Jacob as a hero. This assertion is based the way they are treated artistically, the way characters react to them, and their own actions. This assertion is obviously debatable and subject to change within the show itself, and with this blog I am not trying to establish this point one way or the other. I am trying to clear up what I believe to be some muddy water concerning the issue of good vs evil and white vs black. Please comment with your thoughts!