What’s the difference between an embryo that may one day be conscious and an unconscious person who may one day be conscious? Some opponents of choice say there is none. They say that if it is OK to terminate an embryo, even a blastocyst or a fertilized egg, on the basis that it lack consciousness, then it must be OK to terminate a person who is anesthetized for surgery. After all, they both lack consciousness now, and they both may be conscious at a later time.
But surely there is a useful distinction to be made here. There is a difference between completely lacking an ability and having an ability which is currently suspended. A person who is unconscious, asleep or under anesthesia, still has the ability to be conscious - an embryo has no such ability at all.
I am a person because I have the ability to be conscious - to think, to feel, to experience life. Even if that consciousness is temporarily not in use, I still have the ability, just as I still have the ability to play the cello, even when I am not playing it. When I put down my bow and get a drink or walk around, I do not cease to be a cellist. Current ability is a very useful distinction when thinking about the ethics of abortion.
But what about potential?
I think the best argument against abortion is the idea that if an entity has the potential to become a conscious human, then it has the same rights as a conscious human. The argument states that potentiality itself is what grants a person rights. I will argue that this does not work, although potential is an important consideration.
Do we afford a four year old the right to drive because he currently has the potential to be 16 some day? No. And, if for some terrible reason, we knew a four old would never become old enough to drive, we would not take any rights away from the child because of this difference in potential.
That said, it is valuable to take potential into account when dealing with people. It is sometimes wise to give people the benefit of the doubt, to treat them as the good person they are capable of being, even if they are not acting that way. However this can only go so far. A prisoner may have the potential to become a reformed person, but we do not consider potential a good enough reason to release the prisoner into the public.
But I will not say that potential does not matter as a consideration. Even if a mouse has more consciousness than an embryo, I cannot say that I would necessarily treat them as equals. The embryo’s potential is the reason for this. So potential is an important consideration, but not a strict rule-maker.
And this is the reason why a reasonable pro-choice position makes the most sense. Potentiality is a factor to consider, but not a strict ruler-maker, because the term “potentiality” itself means that the valued abilities in question are not present yet.
The Sanctity of Life
Everyone believes in the sanctity of human life. But there is a difference between “technically alive” and “substantively alive.” Technically alive means the scientific description - which would apply to every living thing from humans to fungi. Substantively alive means life as human beings experience it and value it. We don’t value our lives because we have a metabolism. We value life because we are capable of consciousness. We value life because we can feel and think.
In fact, a good argument can be made that over-valuing “technical life” can come at the expense of “substantive life”. If a single woman, living in poverty with five children, is forced by the state to continue her pregnancy and have the baby, this could undermine the amount of care, both emotionally and materially, that she can offer her five children. If a family is required to pour their material and emotional resources into maintaing the "technical life" of a relative in a vegetable state with no reasonable hope for recovery, then this may result in a net loss of "substantive life" for that family.
So it comes down to this. Everyone believes in the sanctity of life - and the sanctity of human life. But many pro-choice advocates think that being technically alive is not the same as being substantively alive, and because of this there is still a window of time to terminate a technically alive entity before it becomes a substantively alive entity, without grave moral concern.
Because anti-choicers value “technical life” and pro-choicers value “substantive life” - both sides of the argument claim that their position ultimately values life more than the other side.