The same kind of logic motivates people not to accept the infant unless it is wanted and not to want an infant unless it is of "perfect quality". In both cases, the infant isn't wanted for itself; it is wanted insofar as it satisfies the couple's desire. If it is not wanted, news of its arrival thwarts the wishes of the couple. If it isn't perfect, the coming child doesn't respond to the expectations of the couple.
In both cases, the life of the child is in a sort of suspended sentence: its life or death are entirely at the discretion of those who want it.