Re: Lost 5x14: "The Variable"
I assume something Jack & Kate do over the next episode or two has a big effect on the future/safety of the island, so Dan's parents had to send him back, even though it was to his death, so he could get Kate & Jack out into the jungle and tell them his plan. Thus preserving the timeline.
"Everyone's always in favor of saving Hitler's brain. But when you put it in the body of a great white shark, ooohh! Suddenly you've gone too far!"