Maybe what they were getting at is why would you take off knowing that your going to hit a wall or thats how the question reads to me, i.e if theres definate doubt that you would get there then the medics would rather know that before you lifted than tell them en-route, if the weather changes en-route and it's not safe to continue then turnaround, land put them on a land ambulance or go to another hospital but don't kill two more people for the sake of one who could well die anyway. Theres always an alternative.
Thats the advice I was given anyway, and thats the answer I'd give.