Quix, I’ll do my best.
I start from the premise that the fetus is potentially, but not yet actually, a “person” in the sense that it is only potentially a separate individual from its mother. It cannot exist without her - she is literally its sine qua non. A fetus is “parasitic” (probably not the best term, btw) only in this . A newborn, by contrast, can live for an extended period of time without its mother, needing “only” food and water to survive.
Each person has rights, including the right to life and the right to self-determination. The right to life is often, but not always, a prerequisite for the others (for example, we have decided that the dead still enjoy the privilege of conversations they had with their lawyers and doctors while they were alive. Also, in Chicago, they have the right to vote.)
Rights are relative. How to determine which rights take precedence over others is a societal exercise. We have decided, for example, that property rights trump rights to travel unimpeded (I have to go around your land to get to my destination, or suffer the consequences for not doing so).
The question at hand is, “When does personhood begin?” At a minimum, it seems to me that you need an entity that can survive as a separate individual (please don’t bring up conjoined twins) before personhood can attach so that the right to that person’s life trumps the otherwise dominant right of the woman to determine what she does with her body and all its dependant parts. That is, until the fetus can survive on its own, it is a dependant part subject to the whim of the woman. Otherwise you are curtailing the woman’s right to determine what happens to her person, and what it means to her to be a person, in favor of an entity that is not a separate entity, but is in very real fact subordinate. Once the entity is viable, the calculation changes accordingly.
As to whether “viability” means with machines or without, for purposes of this discussion assume it means with. Assume further that “survival” means more than physical survival, that technology would allow a 10-week-old fetus to survive relatively unscathed (i.e., no or mild cerebral palsy, no major systemic malfunctions or malformations, etc.) At some point, that point will move back close to conception. When it does, philosophically I see nothing wrong with saying, “You may not have an abortion because the fetus can survive outside you.” I think that the woman should at that time have the option to say, “OK, if you want this fetus to survive, take it out of me and support it until it can truly live on its own”. While I don’t think this would be practical, it is logically consistent.
I’m curious, for beagledave and JTC and others who believe life begins at conception: do you agree with South Carolina’s program of arresting and prosecuting for “homicide by child abuse” pregnant women who drink or take drugs during pregnancy? See, for example, this site, which is the cert petition in Whitner. If not, why not? I am opposed to it, for the reasons stated in this thread and elsewhere. While I find Whitner’s conduct to be abhorrent, and there are other cases of this, I still think South Carolina has gone too far.
Quix, I hope that helped. If not, it may be because my position is not that well-thought-out or well-expressed. Any defects in the presentation and position are my own. 