Pence in Whose Afraid of Human Cloning presents two arguments against the physical harm argument, the first of which is weak while the second seems much more significant. First, he argues that the idea of "consent of the unborn" is ridiculous because no one can give consent until after he or she is born and is mature enough to understand what consent it.
Second, he argues that the implicit premise is unjustifiable because we already allow couples to try to conceive in lots of ways none of which is guaranteed to result in a healthy child or in any child at all. For example, parents with genetic diseases or using fertility drugs of in vitro fertilization (which has a 15-20% success rate) or even natural conception all have risks and none of which are guaranteed to result in a healthy child. In addition, he counters that many of the things, which parents do on a daily and routine basis, pose risks of harm to the children, even things such as allowing their children to ride in automobiles. In short, we cannot remove all risk from any method of conception and if we set this implicit premise up as the standard, then all bets would be off regarding attempts to conceive a child.
