In the film (I haven’t seen it, or read the book, so I’m going off plot summaries I’ve just read), apparently the donor girl is rarely consulted (when she gets older) about whether she wishes to donate to her ill sister. This wouldn’t happen. Further, there are no points, in real life, where tissue taken from the donor child would harm the child. Note from the above articles that the donor children are 100 % healthy. Not only that, but their birth resulted in a young child not dying. Wouldn’t you want to do the same thing, if you could?
The term ‘designer baby’ or ‘spare parts baby’ severely misrepresent the truth – and you will often find that the people who object to this procedure do not do so on scientific grounds, but on the grounds of their particular religious dogma or gut reaction.
Whilst I believe that Preimplantation Genetic Diagnosis (PGD) should be monitored very strictly, and used very carefully, I have no moral objection to it, and can only imagine how proud the donor child will be when they realise that they are lifesavers!