Well, there are two ways of responding to this question. Firstly, we could start by stating the brutal facts of the novel. As Miss Lucy tells the confused students in class at Hailsham, they are clones and they are clones that have been bred or created for the specific purpose of donating their organs to real humans and dying young. Further support for this view comes from the way that Madame and other characters treat the clones with fear, loathing and disgust.
However, if we consider the alternative viewpoint for one moment, we can come up with the following criticisms. Most importantly, the clones, if that is what they are, seem indistinguishable from humans. They have human emotions, as the novel makes perfectly clear, and are caught up in the same patterns of emotions of jealousy, love and desire as the rest of us. In this sense, there is no difference between the clones and us. In fact, to take this further, the majority of critics of this novel argue that its theme or lesson is actually about humans and how we value and live our life rather than focusing on the rights of cloned humans. Secondly, Ishiguro is very vague and nebulous in his style of writing. There is so much uncertainty that exists in this novel, and therefore it could well be that the clones are not clones but real humans.