A recent post on the subject by William Wildblood helped clarify my views on the broad subject of 'genetic engineering' applied to humans - I mean, in general terms, the ethical questions relating to the technological modification/ take-over of human reproduction.
It strikes me that - from my Christian perspective - the real issue is about parents and children; about families. Our 'ethical' ideal* (that is our moral goal, based upon our understanding of the truth and reality of God's creation) - which we ought to aim for in all things; is that every child is the child of parents.
To repeat: Every child that is born should be the child of a mother and father; conversely no child should be born (or 'made') who is not the child of a mother and father.
The moral nightmare, the stark horror - which modern people have largely lost the capacity to discern, but which ought to be spontaneously obvious - is the scenario of human beings being made without any parents.
Such 'made' people would intrinsically be alone in a world that cared nothing for them as persons. A society that regarded them as made-hence-owned - enslaved 'human resources' at best; but in essence as 'subjects' for whatever experiment, exploitation or torment some person or group wanted to use them for.
(And - it seems clear to me - there are quite a few persons whose desire is to 'own', to have-full-control-of; a child, a person; whom they could 'legitimately' use - or dispose of - for whatever purpose suits their own wishes. This truly-demonic impulse is what lies behind the decades of legal removal of children from their parents' responsibility - to make all children (including those with the most-ideal married parents) both ultimately and proximately wards of The System, of the state bureaucracy, and the individuals that operate within it. Already The State bureaucrats determine whether children be educated, what they are taught and how, their medical treatment, and recently the content of private ideological-religious interactions within the family. Parents who dissent from State authority are increasingly likely to have their children 'confiscated' and subjected to the impersonal, non-loving, abusive regimes of the 'child-care' system.)
If such a moral bright-line were accepted, I think it would entail accepting the fundamental reality and divine authority of the family as God's way of structuring human, and ultimately divine, society in creation.
*Note: By 'ideal' I mean that it is what we, our laws, our social organisation, should be aimed-at. In practice, the family ideal will be unattainable for everybody, all of the time - but knowing and acknowledging the ideal is what enables us to live coherently, with meaning and motivation; aligned with divine creation.