This short film is based on a story by Nick Bostrom.
The moral of the story:
The ethical argument that the fable presents is simple: There are obvious and compelling moral reasons for the people in the fable to get rid of the dragon. Our situation with regard to human senescence is closely analogous and ethically isomorphic to the situation of the people in the fable with regard to the dragon. Therefore, we have compelling moral reasons to get rid of human senescence.
The argument is not in favor or life-span extension per se. Adding extra years of sickness and debility at the end of life would be pointless. The argument is in favor of extending, as far as possible, the human health-span. By slowing or halting the aging process, the healthy human life span would be extended. Individuals would be able to remain healthy, vigorous, and productive at ages at which they would otherwise be dead.