Most debates about abortion begin from the assumption that the fetus is a more or less isolated entity that can be considered in itself, that it is an individual. We talk about when this entity has “life” in the relevant sense, what its rights are, etc., completely ignoring the distinctive trait of fetal life: that it is radically dependent on, and indeed takes place entirely within, an autonomous human being.
This framing concedes the debate in advance, placing the fetus in the series of other entities with human DNA that were belatedly recognized as being entitled to full human personhood, with the attendant rights. Yet the fetus is not at all like those other human beings, because all of those human beings were, though not fully autonomous or independent of others, at least autonomous and independent in the ways considered to be relevant. The fetus’s situation is radically different — qua fetus, it can never display the requisite autonomy and independence, by definition. Its situation changes radically after birth, when it becomes an individual entity separable from its mother (even if requiring vastly more care or medical intervention than an adult), but as long as it is a fetus, it is not an isolatable individual.
Given the unique situation of the fetus, the only coherent outcome of granting the fetus personhood is to deny the pregnant woman personhood. The fact that misogyny often accompanies pro-life positions is not an unfortunate accident — it is necessarily entailed by the pro-life position. The pro-life position takes an autonomous adult human being and makes her into the unconditional servant of another (ostensible) human being. Hence the fact that the pro-life movement is populated either by misogynists or sentimental people who avoid thinking their position through to the end (as when protestors at abortion clinics can hold up signs declaring “abortion is murder” and yet resist the idea that the woman seeking an abortion should be treated as a murderer).
Only in this perspective can we understand the token gestures toward a rape or incest exception (or Senate candidate Akin’s fantasy, apparently shared with a significant number of people, that pregnancy by definition can never happen in cases of rape): our liberal democratic instincts lead even the most conservative among us to grasp for some sense in which entry into the temporary suspension of full human personhood represented by pregnancy in the pro-life view would be a voluntary choice. Yet we all know that’s not really how it works — pregnancy is never fully predictable, never fully chosen in advance. It always takes us by surprise, at least to some extent, and so it can only be “chosen” in retrospect, “endorsed” after the fact.
Hence the only way to preserve the voluntary nature of pregnancy — a position that even the most retrograde misogynist bigots feel compelled to gesture toward in their own ridiculous and offensive ways — is to give women the option of ending pregnancies once they have begun. If you don’t allow that, if you declare that the human fetus is a person with full human rights, then you are necessarily simultaneously declaring that the pregnant woman is not a full human person.
Including the fetus in the series of human entities granted human rights undermines that series by excluding one of its established members. It is thus by definition a retrogressive position and can never be part of a progressive agenda. To be a liberal democrat committed to human rights always and everywhere entails being committed to abortion rights.