The women who rasied Jacob and MIB told Jacob to NEVER enter the cave/light!
So she knew something bad would happen, guardian or no guardian!
MIB died and his soul became the smoke monster.. that was Terry O'Quinn theory, he said so on the Jimmy kimmel show.
And we know that smokey can take form as any dead person from the island.. And not living people becausethey already have a soul ?!?
So Jack didn't have a soul ??