Nobody knows when a fetus attains the status of personhood.
It's possible that the pro-choice community has drawn the line appropriately, at the end of the first trimester.
It's also possible that they have drawn it too late, and are killing persons.
If fetuses are persons, they have a right to life.
There is no right to choose to kill a person for their burdensome presence.
The right does not materialize, just because someone is willing to risk life and limb to make it happen (as in the case of the "back-alley" abortions.
It's possible that I draw the line too early (conception). I only do this out of ethical and intellectual humility, the admission that I know that I do not know. I can't say when it's okay to kill a fetus because I don't know when it attains personhood.
Those who support abortion laws based on developmental stages as determinants of personhood have assumed an arrogant role as arbiters of inalienable rights. Developmental stages are not proof of personhood, or the lack thereof. If you say that a woman has the inalienable right to choose what she does with her body, why should that be any different after 12 weeks. There's no proof personhood begins then. Either she has the right or she does not. If you draw the line, you are assuming you have enough knowledge of fetal personhood to revoke a woman's right to choose, or sentence a fetus to death, as you see fit. If medical science gave us the ability to fully gestate a baby independent of a woman's body, then what? No longer a burden to women, would it then have the right to life? Who would decide, and how?
You don't have to believe personhood or moral value begins at conception. The fact that you don't know should be enough reason to oppose abortion on demand. But to support abortion on demand, you must be willing to say to yourself,"It's okay to take the chance that persons are being murdered, so that women have the right to choose not to be burdened with them in their bodies".
Once you're willing to take that step, I don't see how you can limit or qualify that right. Why do women have to carry a 20 week pregnancy any further, if they don't want to? There's no proof a 20 week fetus has personhood, and people vary in their opinions. If some think 20 weeks is too late to have an abortion, why do they have the right to dictate that to any one else? For that matter, why should viability matter? Is that proof of personhood? Is it enough to revoke that inalienable right to choose to have an abortion?
I know a lot of people think my position is extreme. That doesn't bother me because I think most people put more careful thought into their cell phone plans than they do ethics. The right to life is for all men. That right does not hang on opinion, though obviously, its protection does.