In Britain, one has not reached the political extremes that have occurred in the United States, where in the state of Colorado there is, in the upcoming elections, a ballot on a measure that would define a 'fertilized egg' as a person in the state's constitution. Fertilized eggs and embryos lack any capacity for personhood by any standard of neurological functioning. They cannot laugh or cry, feel frustration or satisfaction, let alone learn or make mistakes. In short, they are nothing like actual children and to declare them to be such, devalues the personhood of actual children and exposes them to concrete harms.
A fundamental principle in our society is the priority of the best interests of the child. Admittedly, this is sometimes difficult to enforce, especially when it conflicts with parental desires. Nonetheless, we should always encourage parents to make this the paramount criterion of their decisions, including the best of interests of a child they expect to have through a pregnancy brought to term. In the context of IVF, parents have achieved unprecedented reproductive choice and control but this freedom should be exercised only in the best interests of the child. It is here where confusion between embryo and child can have its most harmful effects.
Since the embryo does not have the physical or mental capacities of a child, it makes no difference to its existence whether it has a genetic disposition to Downs syndrome or deafness. There is indeed no such entity as an embryo with disabilities. Such a fundamental lack of capacity leads in my view to the inescapable conclusion that an embryo does not have interests. For example, an embryo has no hearing to lose or gain and does not exist in any social context. Therefore it cannot be interested that deafness would exclude it from many sports and prevent it from listening to music. However, a deaf child can be acutely aware of how disability limits her or his activities and choices. I do not believe that it demeans the embryo to say that it has instrumental rather than intrinsic value as long as its essential role in human reproduction is recognized. To deny that an embryo has rights and interests is not tantamount to saying that morally and legally we should be able to do whatever we want with it.
A child, unlike an embryo, has intrinsic rather than instrumental value. A child's value is not determined by the satisfaction or fulfilment that he or she brings to the child's parents. Parental desires and choice cannot trump all other moral considerations when persons seek assisted reproduction. Their expanded procreative choice must still be guided by the best of interests of the child and that means that they should seek to have an embryo implanted that, as far as it is possible to know, will develop into a healthy child in a pregnancy brought to term. They should make use of PGD to maximize their chances of a pregnancy leading to the birth of a healthy child.
Recent arguments for a moral obligation of parents to strive for the genetically 'best child' fail on two counts: There is no consensus on what the 'best child' is and no genetic tests that can reliably predict such qualities as high intelligence or superior musical ability. In contrast, there is very little disagreement on what constitutes an acceptable baseline of health. When no distinction is made between children and embryos, we lose sight of the basic endowment of physical and mental capacities that a healthy child possesses. To insist on the implantation of an embryo at risk for Down syndrome would be as much an embrace of designer babies as the selection of an embryo for a high IQ (intelligence quotient). In both cases the embryo becomes a tool for imposing the wishes and values of the parents on the child.