Should selecting saviour siblings be banned?

By using tissue typing in conjunction with preimplantation genetic diagnosis doctors are able to pick a human embryo for implantation which, if all goes well, will become a "saviour sibling", a brother or sister capable of donating life-saving tissue to an existing child. This paper addresses the question of whether this form of selection should be banned and concludes that it should not. Three main prohibitionist arguments are considered and found wanting: (a) the claim that saviour siblings would be treated as commodities; (b) a slippery slope argument, which suggests that this practice will lead to the creation of so-called "designer babies"; and (c) a child welfare argument, according to which saviour siblings will be physically and/or psychologically harmed.