"Forced birth"

Abortionists sometimes brand prolife legislation as "forced birth"–as though there's something inherently objectionable about that. Let's consider the permutations of that objection. What exactly is the objectionable principle?

i) Is the objection that no one should ever be forced to do anything they don't want to? Consider individuals who voluntarily incur a financial obligation, like using a motel, dentist, or rental car. Is it wrong if they are "forced" to pay for the goods and service they used? That's hardly plausible as a general principle.

ii) Is the objection that no one has a claim on the use of someone else's body? If so, consider some counterexamples: Suppose somebody in a wheelchair needs help getting over the sidewalk curb. Strangers have a moral obligation to help him (or her). In that sense, someone can lay claim to the use of another person's body. 

Likewise, if a child falls into a river and is about to drown, strangers who know how to swim have a duty to rescue the child. Once again, that's a moral claim on the use of someone else's body.

These are very limited examples, but they demonstrate that you can't rule out as a matter of principle a person in need having a claim on someone else's physical agency. 

iii) Is the objection that while we can be forced to do something or undergo something if that's a consequence of something we consented to, we can't be forced to do it or undergo it absent consent at the outset. If so, what about men who are drafted to fight in war? That's involuntary. Moreover, many of them die, are maimed or disabled as a result of military service. Surely that's at least as traumatic as a rape victim given birth. 

iv) Apropos (iii), is the objection, not to "forced birth" in general, but to "forced birth" in case of rape victims? Is the objection that it's grossly unfair to make pregnant rape victims carry the child to term. 

If so, I agree that it's unfair to make a rape victim go through that ordeal. However, it's possible for something to be unfair, yet still be a duty. 

Suppose I have a teenage brother who's disabled in a cycling accident by a reckless driver. It's unfair that he suddenly requires special assistance from me. I had my life planned out. Now I have to make adjustments and sacrifice my dreams. But it doesn't follow from this that I don't have an obligation to help out my disabled brother, even though the situation was forced on me (indeed, forced on both of us).

Suppose my wife cheats on me. She has a child by another man. At the time I don't know about the affair. I don't know the child isn't mine. 

Suppose I find out at a later date. Suppose, moreover, that when the child turns five, my wife leaves me with the child. She divorces me and moves in with another man. 

I'm "stuck" with a child I didn't father. That's "unfair". But at this stage, I'm the only father the child has ever known. It would be psychologically damaging to the child to put him up for adoption at the age of five. The child reminds me of my wife's affair. Should I withhold my love from the child because it's unfair that I was thrust into this situation? Surely not!

v) Admittedly, moral arguments have no traction if you're addressing a moral nihilist. There are people who will reject these examples because they're nihilistic. And that's one of the dangerous things about atheism.