It seems every so often I run across someone on Facebook (rarely in personal activism) who asserts that we must convert people to Christianity in order to end abortion, or that we must share the Gospel at all times with people, whether or not we make pro-life converts. To do anything less goes against God's teachings.
This may sound super spiritual on the face of it, until you stop and consider that, as Augustine said, "wherever truth may be found, it belongs to his master" (On Christian Doctrine, II.18.28). Or as it is commonly paraphrased, all truth is God's truth. Whenever we share the truth about abortion, that it is the unjustified killing of an innocent human person, we are sharing God's truth. Now, it's possible that someone would only be converted after you share the Gospel with them and they come to understand the universe as God does. But it's also very likely that someone will not take the Gospel seriously until they hear a Christian give a reasoned defense of one of their positions in another sphere of knowledge.
I, myself, have met people who said they did not come to Christ until after they became pro-life. In fact, this is true of Bernard Nathanson, an atheist physician who founded NARAL. He became pro-life while still an atheist, then converted to Catholicism later in life.
I have been attending the Clarkson Academy in Battle East Sussex, England. At this conference Michael Sherrard gave a presentation. He is the pastor of a church, and one of the members of his church asked a friend from college if he'd like to attend church with her one Sunday morning. The parishoner's friend was an atheist who agreed to go to church with her because it was important to her. While there, Mike gave a presentation on the pro-life position. The friend was highly impressed with Mike's rational defense of the pro-life position, so the rest of the time the parishoner had with the friend while the friend was in town, he spent time asking important questions about Christianity. His parishoner's friend's interest in Christianity was only piqued because he heard Mike give a reasoned defense of the pro-life position.
The cold reality is that if we want abortion to end, but we think we have to always share the Gospel in order to do it, we're going to turn many people off. We'll never end abortion that way. Scott Klusendorf, in another presentation, reminded us that even the Bible says this: narrow is the way and there are few who find it. We could never possibly hope to end abortion if our only goal is to share the Gospel. If we really want to save babies, we have to be intentional about when we give a reasoned defense of the pro-life position, and when we share the Gospel. Many of my conversations on abortion naturally lead into discussions of ultimate reality, where morality comes from, and so on. But if that was my only goal, I'd never see an end to abortion.