That argument only holds if you agree that the fetus has no interests, preferences, or ability to suffer. Anti-abortion activists would probably argue that this is not true, just as they claimed that Terri Schiavo was fully aware of her surroundings despite most of her brain being rotted away.
True. But then again, all that requires is expanding the scope of the utilitarian argument to encompass the entire moral community in which the mother lives. An unwanted pregnancy does not just negatively effect her, but her family unit, in that a pregnant female (or one with a young child given the state of adoption in tbhis country) cannot produce as much energy (read: resources) as a non-pregnant/post-natal mother. A baby that is unwanted (and statistically unable to be cared for) puts strain on the social infrastructure and if they are in an unstable environment (like being raised in a poor neighborhood by a mother unable and unwilling to care for it) they may grow to engage in high-risk behavior in order to maximize their reproductive success. This hurts everyone.
Even if we assume the fetus and a baby are equivalent, they have interests, and wants and sapience, it still does not follow, because under a utilitarian ethical system, unwanted babies under many many many circumstances are OK to kill. Provided the momentary suffering of that baby and the total aggregate alleviation of suffering is the best possible balance of good and bad consequences.
A baby is considered to have an inherent claim on its parents, so this strict separation of rights is a questionable premise if you believe that a fetus and a baby are equivalent. Which is exactly what fundies believe.
That is an argument that in countless debates with pro-lifers making this very point I have not heard. It interests me. I know you detest rights-based theories to a degree (as do I due to metaphysical problems) but if you could elaborate that would be awesome.
I would posit that the inherent right of a living baby to impose obligations upon its parents is not absolute, in fact our society has recognized that under many circumstances that right can be over-ridden by the parents desire to not have a child, such as provisions that they be allowed to abandon said children at safe-zones, give them up for adoption, etc. As a result it is not so unreasonable to say that said right does not extend to physical enslavement of the mother in order to use her uterus. Even if we accept a priori that life and metaphysical humanity exist from the moment of the fusion of gametes. Basically, it does not follow and is such, if applied in an actual argument, a non-sequiteur.
If we want to argue equivalence, the only way to do it without being ripped apart on the basis of neurology is to argue that there is something intrinsically special about human DNA, or to argue for some other metaphysical quality like the soul. Both of them open themselves up for massive metaphysical and empirical problems.
