I completely agree with the comment you are responding to, but it is an argument that actually changed my position relatively recently. I used to believe in the "well, if you believe it is a person, then abortion is murder" argument, but I believe the bodily autonomy argument is much stronger.

If you have a child, and you are the the only good potential donor match, and that child will die without, say, a bone-marrow transplant, you are not forced to donate your own bone marrow. Saying "You totally have the legal obligation to provide for your children, if you have them, and that almost always involves using your body in some way" is a poor analogy that really doesn't encompass what it is to have another being living inside you.

That's why I think the "viability" standard is the only one that makes sense, and also why that as technology has improved that I think the cutoff date for abortion should be lowered to the new age of viability. Any human should have the right to remove another from their own body. In the case of a child, if we have no technology to allow that child to survive outside the mother, so be it, but I think the much better analogy to forced birthing is actually slavery.