I think the point here is that they’re willing to “sacrifice” a few 10-year-olds if it means saving tens of thousands of other children aborted yearly for what they see as lesser reasons.
Though I don’t agree with their view, if a religious person genuinely believes that life begins at conception and sees no difference between ending the life of a 10-day-old embryo and a 10-year-old child - because they believe both lives are equally valuable - then I can’t entirely fault their reasoning. In this case, the issue lies with their false, unscientific religious beliefs, not necessarily their stance on abortion. If you truly believe that life starts at conception, being against abortion is a perfectly logical position to take.
But you need to understand that to a religious person this is a completely insane thing to say. You can't simply kill a person just because you don't want to be inconvenienced by having to take care of them. They see abortion as an equivalent to killing a 3-year-old who refuses to eat their vegetables.