I think you may be confusing someone "doing good" and someone "being good". Jacob is like a good parent who wants the best for his kids (his recruits). That doesn't mean the kids find the parent to be good. Jacob wants the best for us; that we stop killing each other. He is well intentioned, not necessarily being good. And, he brings people that are broken to the island, answering their prayers, giving them a chance to find meaning in their lives or at redemption. "Here, the past doesn't mean a thing".

MiB doesn't give a damn. His intentions are evil and nothing good can come from it. What he told Ricardo was, in effect: You don't know if he or I have your wife and you say you don't want to kill someone because that is what put you in trouble but, if you want to see your wife again, you must kill Jacob.
Evil Incarnate.

Also, MiB's word was supposed to be good forever but, now that Jacob's dead, MIB didn't answer Richard's plea. He didn't give a damn.

Think of it another way: Hurley has always been the audience's moral compass. Some followed the man of faith, Locke, and others followed the man of science, Jack. Hurley was never blinded by faith or captivated by science. He relied on common sense. As an example: A hatch marked quarantine wasn't a good idea to open. Which side did Hurley pick? Jacob's. Hurley HAS to be on the side of good.

Is Jacob playing a long con on Hurley? I suppose you could still think so but Jacob's MO has always been to leave one's free will, not to dirty his hands. This whole series would be a terrible waste if it was a practical joke played on the one character who never wanted to lead, never wanted anything for himself. It may have to wrap up in such an odd way because they are flirting with the notion that Jacob/God is the source of all Man's misery.