Just speculation based on the previews for next week:
If the members of Danielle's party became violent as part of the early stages of the illness, she may have needed to kill them to protect herself, her child or other not-yet-infected members. Besides, we don't know that she killed them all. She could have killed some, while others succumed to the illness.
Its also possible that if the illness is a biological weapon of some type, it might have been engineered to increase peoples' natural aggression levels, so the enemy would fight among themselves. We would kill someone who is sick in self-defense.
The reason I think this could be the case is my assuption that the black man in the previews is Rose's husband. Based on Rose's conversation with Jack, you get the impression that her husband is a good, even gentle, man. Why would he become aggressive towards Michael, Sawyer and Jin with no cause or imprison the girl that Jack met at the airport bar?
Again this theory has huge chunks of speculation in it. But that's the great part of this show... coming up with possible theories.
Duey... I'm not sure how the Black Rock would fit into this theory. Maybe it was salvaged by the Others or maybe it just shipwrecked there during a tide wave and isn't related to the hatch. I don't know.