“Creating new people, by having babies, is so much a part of human life that it is rarely thought even to require a justification. Indeed, most people do not even think about whether they should or should not make a baby. They just make one. In other words, procreation is usually the consequence of sex rather than the result of a decision to bring people into existence. Those who do indeed decide to have a child might do so for any number of reasons, but among these reasons cannot be the interests of the potential child. One can never have a child for that child’s sake.”