Saviour Siblings

I saw a TV news article the other day about families who have children that need special treatments requiring genetic material such as stem cells, these families are having other children that will supply the needed material. The article was actually about the UK having passed a law allowing this to happen. I have a son and wouldn't want him to have any disease or condition but if he did I can't say I would have another child to supply what is needed. According to New Scientist (http://www.newscientist.com/article/dn6195-saviour-sibling-babies-get-green-light.html) "One family in Britain, the Hashmis, had earlier received explicit permission from the HFEA (Human Fertilisation and Embryology Authority)to try and create a baby whose cord blood could be used to treat a sibling with the blood disorder, beta thallassaemia.

Another family, the Fletchers from Northern Ireland, are now hoping the procedure can be used to create a donor for their son, Joshua, who has a condition called Diamond Blackfan anaemia." This would seem in my opinion to create some ethical dilemmas. Under the circumstances what is to prevent one child from using his or her status as a "lifesaver" against their sick sibling? What is to prevent the family from thinking of the "lifesaver" as nothing more than a means to an end. Would these families have had another child if this need didn't exist? Is the need the only reason they had another child? I find it hard to believe that both children would get equal treatment. What are your thoughts?