Everyone is so hung up on the fact that the Man in Black is the smoke monster, but did anyone consider that Jacob could be a smoke monster also. We have no reason to believe that the MIB and Jacob are not the same type of being. It is completely feasible that they both have the ability to change into the smoke monster.
If we think logically about this, in 1988 when smokey kills the french people, it comes out of that hole in the wall. Why would smokey want to protect the temple of Jacob worshippers? I think it may have been Jacob that killed the french people.
Also, it appears that MIB was imprisoned in the cabin by the circle of ash. Granted we don't know how long he was trapped there, or if that was even him at all, but assuming it was, that would mean that a different smoke monster would have been terrorizing the Oceanic 815 camp when they first crash landed.
It is not unreasonable to think that Jacob would kill people as the smoke monster. After all, the Others constantly kill or threaten to kill people who aren't on his list or who otherwise don't belong on the island.