Knuckles - re "I think if you gloss over the technical problems with transplants"
You can't "gloss over", though. The whole book is based on the idea of clones created for organ transplants. If the book doesn't solve the inherent problems with that idea one way or another and in a credible way, than it makes no sense. How do you gloss over a book that makes no sense? I can't.
For all the flack it gets, SF is a difficult genre for this very reason: You must create a world that doesn't exist, AND you must make it feel real, which means that its foundations have to be credible. Never Let Me Go fails at this. Miserably.
"... the whole point is their passive acceptance. Is it because that's what they were brought up to expect, or is it because they have no souls?"
That is another major part of the plot that makes no sense whatsoever. Never in the history of the world has a group of morons just accepted that they will die horribly painful and cruel deaths at the hands of other people.
You can be brought up to expect a terrible fate but you will still do your absolute best to avoid it. Generations of slaves in America were brought up to expect mistreatment and an early, painful death. Yet many of them escaped despite a slim chance of death, fought and died rather than submit to this fate.
It is in the nature of every animal, down to insects, to avoid suffering and death. Even fucking sea cucumbers will remember a painful circumstance (like a hand rubbing salt on them) and avoid it the next time. And we are expected to believe that there has never even been a single clone, made of exactly the same DNA as the rest of us, who even tried? 
Oh and "no souls" just made me laugh. There isn't a single mention of any spiritual reason for this docile acceptance. And of course none of us actually have a soul 
There are many brilliant SF masterpieces who create very detailed and utterly credible universes. It is shocking that such a simple book who just had to explain a bit of cloning and docility failed so miserably.