The Borgified Corpse wrote:
More significantly, in "Voyage of the Damned," I thought they were saying that, if the ship crashed, its engines would explode and cause a chain reaction that would wipe out all life on Earth. But in "Turn Left," when the ship does crash, only London seems to have been affected.
Evidently, Astrid, Midshipman Frame and Bannakaffalatta were able to minimize the destruction somehow, but at the cost of their own lives.
Similarly, someone in America (Grace Holloway and Chang Lee?) confronted the Adipose, but they weren't able to stop them from converting millions of people and escaping.
That also didn't make sense to me. I'd gotten the impression from "Partners in Crime" that, had the Doctor & Donna not exposed the Adipose's operation, they would have been happy to operate in secret, merely harvesting a little fat at a time from people who could afford to lose it and wouldn't notice anything untoward.