i) There's a striking parallel between abolitionism and pacifism. Abolitionism is to pacifism as prolife philosophy is to military ethics (e.g. the double-effect principle).
Pacifism leads to moral paralysis. So petrified are pacifists by the "problem of dirty hands" that their phobia about moral contamination generates moral dilemmas for their position. Consider some stock objections to pacifism:
However, the pursuit of purity can also be criticized for being other-worldly, unrealistic, and utopian...The pacifist who seeks, regardless of the actions of others, moral purity often requires subsidizing or free rides on the moral impurity of others.
The pacifist who claims that he has no duty to intervene in saving others affairs treads a precarious moral path here; the immediate retort is why should the moral life of the pacifist be morally more important than the life of the threatened innocent? For the sake of his own beliefs, could the pacifist consistently ignore the violence meted upon others?
That's eerily similar to abolitionist scruples and conundrum. Consider this complaint:
Abolish Human Abortion
Making an exception to murder children so long as they have not yet lived in their mothers' wombs for 20 weeks is a wicked compromise with the culture of death.
ii) That's a half-truth. AHA is right to see an evil in this setup. However, it misidentifies the culprit.
Prolifers are analogous to just combatants who are confronted with a human shields. Let's take a couple of real-world examples:
One of the reasons for the firebombing of Japanese cities was the decision by Japanese leaders to disperse key manufacturing facilities across urban areas, rendering European-style daylight bombing raids essentially fruitless. We were faced with the terrible choice between area bombing and leaving much of the enemy’s war machine essentially unmolested — in the midst of an existential struggle for our existence. We chose area bombing.
A more recent example is how Hamas deliberately stockpiles weaponry in civilian population centers. In both cases, the enemy plays a game of chicken. The enemy gives you a forced option. It dares you to exercise the right of self-defense by killing innocents.
Now, there's definitely evil to be seen in that situation. It is not, however, those who attack military installations nestled in civilian population centers that commit evil; rather, the enemy did evil by maliciously narrowing the options to two terrible alternatives: either surrender to the enemy by refusing to defend yourself against jihadist attacks or else defend yourself at the cost of killing noncombatants.
It's not as if Americans were trying to kill Japanese civilians. Rather, the Japanese authorities went out of their way to make that unavoidable. Same thing with Hamas in relation to Israel.
Likewise, it is evil when the power elite imposes a choice between saving some babies and saving all babies. However, prolifers aren't guilty of evil. Rather, it is evil to confront them with those alternatives–just as it is evil to taunt soldiers with human shields. But within those parameters, it would be evil to save no babies if you could save some. Pacifists and abolitionists suffer from a failure to appreciate that omission can be a source of moral compromise no less than commission. Inaction doesn't avoid the "problem of dirty hands."
In that situation, prolifers are basically operating from the double effect principle (or some refinement thereof). That's not a "wicked compromise." It is wicked to be put in that situation. But given that situation, it is not wicked to save those you can.
iii) Indeed, we can mount an a fortiori argument: If, in a human shield situation, it is morally licit to sacrifice some innocent lives to save other innocent lives (when you can't save them all), even though the requires the just combatant to directly kill some innocents, then it is morally licit to sacrifice some innocent lives to save other innocent lives when the prolifer isn't killing anyone, but preventing some from being killed. If the greater is permissible, then lesser is permissible (a maiore ad minus).
For more on the double effect principle: