The MIB may not be 100% evil, folks.
Let's not forget the following:
Ben and Richard have killed, kidnapped, and manipulated everyone they have come across throughout this entire series; all under the instruction of Jacob.
We now know that Jacob is responsible for bringing people to the island (against their will, might I add) in the first place. MIB has expressed how he thinks this is unfair (see "The Incident" parts 1 and 2).
Everyone the MIB has killed has been killed for the sole reason that they have stood in his way. Everyone has been given a chance to spare their own life.
I'm not saying that he ISN'T evil, but I'm just pointing out that everyone has done their fair share of dirty deeds.