This argument is in fact not my own. It was first introduced in a 1990 book called Moral Question of Abortion, by Stephen Schwarz. It is commonly referred to as the "SLED" argument, because it begins by using the word sled as an acromyn, with each letter in the word referring to one key difference between a fetus and a newborn infant. While I will rely on the formula of the argument, I'll do so in my own words.
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Size: One obvious difference between a fetus and a newborn infant is size. One might say, "how can something that small be a person?" But is it size that makes us human? Of course not. To say that would also imply that adults are more human than children, and that tall people are more fully human than short people. Men are typically larger than women, but they are not more human. I saw this bumper sticker just the other day:
Level of Development: Let's talk about this. An embryo in the very earliest stages doesn't have a lot of the things an adult has, including a functioning brain, the ability to experience pain, a beating heart, fingers, toes...the list goes on. But human value is not based on abilities, what a person can or cannot do. Again, brain damage does not make someone less human. Nor does a lack of fingers, nor the lack of an ability to feel pain. And one must consider the difference in development between a toddler and an adult. Despite the significant differences in both ability and appearance, the life of the toddler is no less valuable.
Environment: You might think this one would be a no-brainer, but thinking persists that because a child remains in the womb, it is not yet a person. "Location, location, location" certainly matters when we're talking about real estate values, but it has nothing to do with human value. Moving a few inches down the birth canal does not immediately make one human. Where you are and where you live doesn't give you value. That's basic human rights.
Degree of Dependency: Let's think this one through. An unborn child is absolutely dependent on its mother to live. That's true. However, we must allow that as science advances, younger and younger babies are capable of surviving outside the womb. A child that would not have been able to survive outside the womb twenty years ago might do quite well today. So does the child have more inherent human value simply because technology has advanced? Absurd. You may choose to argue that even that child could not survive without technology, but if you do, be prepared to give an answer to others dependent on technology like pacemakers and the like. Further, it's not as if a child is not dependent on its mother once it's been delivered. You couldn't just leave it alone outdoors and expect it to take care of itself. It's absolutely dependent on others for its care. So are most young children, but we wouldn't question the value of their lives, would we? Does being less dependent make one more valuable? Of course not. I could argue that none of us (or at least very few) are completely independent on each other. Dependency does not negate human value.
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That's the SLED argument. I'm anxious to hear your feedback. And don't wander too far. Part three of this series on abortion will be coming soon.
-Solid