There are many arguments against abortion. Some are strong, some are weak. Many Christians say they’re against it because the Bible or the Church tells them it’s wrong.
That’s fine, but those answers aren’t going to convince many pro-choicers. You need to rely on logic and testimonials from people harmed by abortion.
Here is the best logical argument against abortion.
Premise 1: It’s always wrong for big, strong people to kill little, weak, innocent people.
It’s hard for pro-choicers to deny this, especially since many of them admirably advocate for helping poor people, migrants and victims of violence. It’s human nature to protect those who are weaker than us.
Premise 2: The unborn are little, weak, innocent people.
This is often where abortion advocates disagree. They may regard unborn children as a clump of cells, not living human persons.
However, unborn children are alive. They meet the scientific criteria for a living being. They’re also members of the human species.
Some pro-choicers will say, “They’re not human, they’re fetuses.” They speak as if a fetus was the name of a species. But a fetus identifies a stage in the life of a member of a species, not the species itself.
Further, it’s hard to deny that the unborn child is a person. Challenge your pro-choice friend to explain when they think an unborn child becomes a person. Typically, they’ll mention a random stage in development or say they don’t know.
If it’s the latter, that’s an admission that abortion may be killing a person. If it’s the former, point out that they may inadvertently be justifying murder of certain types of people. For example, saying a child becomes a person once they can live outside of the womb makes their personhood dependent on location and degree of dependence. But does that mean it’s less wrong to kill a toddler than a young adult since the former is more dependent on the mother?
Conclusion: It is always wrong for the strong to kill the unborn.
If premises 1 and 2 are true, then this conclusion necessarily follows. If abortion supporters deny the conclusion, they need to refute one or both of the premises.
Don’t let them distract you with logical fallacies, such as trying to silence pro-life men by saying, “Men have no right to speak on abortion.” Keep them focused on the personhood of the unborn.