A problem I have seen among US 'pro-life'/ anti-abortion Christians is a false assumption about the universality, the 'natural law' validity of their intuitive sense of abortion - and indeed infanticide - as evil.
Christians talk as if it could be assumed - for instance - that non-Christians regard abortion as morally equivalent to murder.
And when Christians argue that especially late abortion is equivalent to infanticide (i.e. killing of a newborn by his or her mother) - the assumption is that non-Christians regard infanticide as morally equivalent to murder.
Yet I think it is a simple fact that the equivalence of abortion and infanticide with murder are not spontaneous human intuitions, but are rather specifically Christian convictions.
It seems that these convictions and intuitions have not been shared by many or most people in history, as they are not shared by many people in the modern world.
The 'pro-life' intuition and stance is distinctively (if not exclusively) Christian - and this insight ought to be the assumed basis for interactions between Christian and non-Christian regarding these matters.
In The Rise of Christianity, Rodney Stark describes how the immortality of abortion and infanticide was part of a variety of pro-natalist doctrines that characterized the early Christians, and which operated within the burgeoning society of Christians - but distinctively in that sub-group of society.
Thus, ancient Christianity grew rapidly by exponential natural increase (as well as by conversions), in a Roman society where women increasingly strove to avoid childbearing and families were kept small or absent.
It is easy to find many other example of ancient civilizations that were also anti-natalist. But more pertinently, perhaps, records of pre-civilization, simple hunter gatherer societies also frequently practice infanticide - usually by 'exposure' (abandonment of the new born child by his or her mother); and therefore would presumably practice abortion if the technology was available.
My factual point is that humans are not innately/ spontaneously/ naturally averse to abortion or infanticide - the wrongness of these activities is not a universal moral prohibition as with murder (although that prohibition of murder may not include strangers). Pro-life is not a human universal morality.
What does seem to be a human universal is that abortion and infanticide are regarded as a 'bad thing' - although not as bad as murder: and therefore something that naturally makes the mother feel bad...
And therefore something to be avoided if possible, and done only when it is the lesser of evils. Abortion/ infanticide are certainly not something to celebrate or to advocate.
My moral point is that Christians should not assume that non-Christians feel the same abhorrence at abortion or indeed infanticide.
The strongly-motivated avoidance of such behaviour is part of being a Christian, but not part of being human. And the difference is one reason for the intransigent nature of these policy disputes.
Another problem is that there is a difference between setting up and justifying laws - which must be clear and categorical, especially in alien, massive and bureaucratic societies such as ours - and the specific, distinctive moral realities of exact situations and circumstances.
Real morality is about specific issues - each unique; not about absolute and generic prohibitions of broad categories of events. This is why all truly just systems of law have provision for the interpretation of categorical systems by the 'judgment' of a wise and good human judge. The ideal judge bridges between legal categories and the unique circumstance.
Failure to recognize this specificity of morality in religion leads to cold-hearted, anti-Christian 'legalism' or Pharisee-ism in Christianity. And this insight ought to apply to abortion and infanticide, just as it does to arson and murder.
Our ultimate problem is that we almost-wholly lack wise and good judges, as we ourselves ("the masses") lack wisdom and goodness.
And bad Men (wrongly-motivated, cowardly Men) cannot be made good by system, by imposing laws or regulations - nor by abolishing them.
System can make us worse - which is why it is a major tool of Satan; but System cannot (here and now) make us better.