In 1980 Mary Anne Warren wrote: “Some human beings are not people, and there may well be people who are not human beings.” Warren suggested that fetuses should not be recognized as people and should not be granted rights. She also suggested that one day when robots possess qualities like intelligence and self-awareness they should be regarded as persons. It is not an inconceivable leap from fetuses to newborns (it is just a few inches from womb to world).
The problem is how we define “person.” The attempt to come up with a moral category for person is blighted by sinful attempts to do it without reference to the Person who made us. We know we are persons by virtue of our being made in the image of the Person who made all things.
Infanticide, if given legitimacy would be a great evil, perhaps the greatest.
Most of us know someone who might not have counted, one whom our authors call “a moral irrelevance.” Irrelevant to some, but not to God. To God, they are people whose person-hood was certain before the beginning of time.