Designer Babies- For love or science?

When we read about the babies being made to help save the life of a child I thought that it was an alright idea but what would you tell that kid when they are growing up. That if they are growing up and the sister or brother says something like "Your the one who was made to save me" or something like that, that kid might get mad and ask the parents and the parents will have to tell the truth and see how the kid reacts. If I was that kid I would probably be mad and sad, I would have mixed emotions about it.