By sheer coincidence I first saw Similitude
around the same time that I first read Never Let Me Go
. In that book, clones are raised knowing when they grow up their organs will be harvested to save "real" people. They just go along with it, because that's just how it is and they've been raised to believe that's their purpose.
You can say it made a difference because Sim chose to die to save Trip, but did he really? Weren't they sort of prodding him toward that choice his entire life?
I can't see how it's ethical to create and kill one sentient being to save another, even if that being does go along with it.