> Very simply, every "a fetus is a person and the state should force it to be carried to term" is no different from "if a person needs a kidney or they will die, and you are a match for that person, then you are required to give them your kidney".
Not sure if you're intentionally referencing Judith Jarvis Thompson's most famous (and in my opinion, greatest) essay with this comparison, but yeah, this is a common metaphor. The sick violinist and all.
But I think you may be discounting the role of viability too quickly, both in theory and in practice: in theory, because some bioethicists (I can't remember if JJT specifically falls into this camp, it's been a while) draw a distinction between terminating a pregnancy and actively destroying a fetus. They'd argue that it's fine to remove a gestating fetus from your body, but not so fine to tell the doctor performing the d&c "and make sure it's good and dead afterwards!" Under current medical practice, there's no practical difference between removal and "killing," simply because it's impossible for an underdeveloped fetus to survive outside the human womb... for now... dot dot dot...
And in practice, because fetal viability is often used to draw abortion boundaries in more permissable jurisdictions who don't restrict it outright. "Late term abortion" is a complicated issue, probably ill-suited for this forum, but viability is generally why you can't abort a healthy fetus three weeks before its natural due date.