WARNING: I usually am not this direct, because I want to live up to the the second half of 1 Peter 3:15 as a Christian apologist. However, this is an issue that warrants a little force. Please forgive my strong words and know that I only say this because I care.
Abortion is not a political issue, it's just an issue that has been politicized. What's more, the pro-life position is not one that can only be reasonably held on the basis of Bible verses. The separation of church and state mantra, which is given regularly by pro-choicers as a way of sidestepping the real discussion, is just a smoke-screen. To make the point, here are two arguments (one mine, and one from Stephen Schwarz) that demonstrate that no thinking person (Christian or otherwise) should support the pro-choice movement. They demonstrate that abortion is a bad . . . nay . . . a bigoted, narrow-minded, backwoods, illogical, immoral, animalistic activity. See what you think . . .
First we have to understand one fact of which pro-choicers are painfully unaware. Among pro-choicers who are the most knowledgeable about this issue it is uncontroversial to admit that from the moment of conception there is new human life. Take the words of Peter Singer for example:
“It is possible to give ‘human being’ a precise meaning. We can use it as equivalent to ‘member of the species Homo sapiens.’ Whether a being is a member of a given species is something that can be determined scientifically, by an examination of the nature of the chromosomes in the cells of living organisms. In this sense there is no doubt that from the first moments of its existence an embryo conceived from human sperm and eggs is a human being.”
In fact, Planned Parenthood use to be very straightforward about this. In a 1964 pamphlet discussing birth control, the group accidentally let the unborn cat out of the bag, saying, "Absolutely not. An abortion ends the life of a baby after it has begun.”
Even the late great atheist, Christopher Hitchens (an atheist pro-lifer) explained, “Unborn child seems to me to be a real concept. It’s not a growth,” he says, “you can’t say that the issue of rights don’t come into question.”
I'm no scientist, but here is the issue. Sperm cells represent male-human-biological-material, and eggs represent female-human-biological-material. When conception takes place the result is new-human-biological-material. In other words, new-human-life. If you are a pro-choice advocate and want to debate this issue then you need to hit the books (even thoughtful pro-choice propaganda material). This is not a controversial claim, but an accepted fact. The question is whether the living material has "personhood" or represents a new person.
With this clarification, we are finally ready to consider two powerful arguments in favor of the pro-life position (and they are not religious arguments).
THE S-L-E-D ARGUMENT - Stephen Schwarz put together what is in my opinion the best case against abortion that has ever been outlined for the masses. the word SLED is an acrostic. Those that are familiar with my ministry know that acrostics are my guilty pleasures.
S is for SIZE - If we are to determine that the unborn are not persons because of their sizes (i.e. they are only small collections of cells rather than full grown adults) then the argument of the pro-choicer proves too much. The claim would amount to saying that the smaller a human life is, the less it should be considered a person. Thus, short people are less whole persons than tall people. My wife would object to the notion that because she is head and shoulders less tall than I am, she is less of a complete person. I actually prefer petite women, so I would object on preference anyway. Yet, we all know that the size of a human life does not dictate the degree of personhood. We cannot bigotedly discriminate based on size.
L is for LEVEL OF DEVELOPMENT - A common pro-choice claim is that since the unborn are not just small, but "collections of cells" then they are not actually persons. In other words, they are less developed. They are not totally developed human life, but merely, potentially totally developed human life. The problem is that what can only be meant here is that the unborn are potential adult humans, but not yet adult (or fully developed). However, this again would prove far too much. My six year old daughter is also not a fully developed adult human. She is a potential adult human. Her level of development is at a reasonably early stage. Is she less of a person? Clearly not. In fact, my three year old daughter is even less developed than my six year old. The level of development has nothing to say about personhood. We cannot bigotedly discriminate based on level of development.
E is for ENVIRONMENT - The most used response in favor of abortion is that the unborn are not persons because of their environments. They are in the womb rather than outside of the womb. Because of this unusual location they are said to be potential persons, but not actual persons. The problem is that in no other aspect of life do we consider someone less of a person because of their location. Are Africans less persons in the eyes of North Americans because they are in a different environment? Does one's status of personhood change based on which room of a building they are inhabiting? Naturally, the answer is of course not. We cannot bigotedly discriminate based on environment.
D is for DEGREE OF DEPENDANCE - Since the unborn are dependent on the mother for survival (via nutrients, amnionic fluid etc.) the pro-choicers often imply that they are not persons and it is okay to terminate them at the will of the mother (who is, after all, supplying the means by which the unborn survive). But what about the disabled, the elderly inhabiting assisted living facilities, or anyone else who depends on others for survival? Do they also cease to be persons upon developing such needs? The answer is, no. They do not. We cannot bigotedly discriminate based on degree of dependance.
Thus, pro-lifers are justified in saying that abortion is not only wrong, but a bigoted, narrow-minded, backwoods, illogical, immoral, animalistic activity. At least, we would consider it to be all of those things upon applying the same logic to any other human life. Yet, I have another argument for the consideration of pro-choicers.
THE BOOTH ARGUMENT- If one is still hesitant to agree that on the SLED case we should consider the unborn persons from the moment of conception, an argument in favor of erring on the side of caution should seal the deal. Imagine that before you stands a doorway, and in that doorway is a booth (like a phone booth, but with no windows). You want to pass through the doorway, but the booth is in your way. Perhaps you desperately need to get through the door, or conversely you may just wish to pass through the entry as a matter of convenience. Yet, you have no way of knowing whether or not the booth contains a person (in this case an adult man). The only way to pass through the doorway is to explode the booth, possibly killing its human contents if there is any. Now ask yourself whether you would be justified in going ahead and exploding the booth. At worst, you would be guilty of murder, and at best - reckless endangerment.
This comes to bear on abortion when one considers that at any stage of development the fetus may or may not have personhood. Naturally, a Christian will often contend that the fetus is definitely a person, but I'm framing this case for those who do not have those delimitations. If one does not accept the truth of Scripture, then the best they can do is say, "I don't know if the fetus has personhood at the moment of conception, but it might." Any attempt to argue that it certainly does not have personhood is merely based on an arbitrary belief. So the fetus becomes like the booth. The woman seeking to have an abortion can never say with certainty whether or not she is murdering a person, because she can never make an objective determination of whether or not the fetus is a person. Thus, if she "explodes the booth," she is guilty of murder (at worst) and reckless endangerment (at best). It is much safer to err on the side of life in such a case.
It is my hope that if you came to this article as a pro-lifer you will share it with others, and if you came as a pro-choicer you have seen that it's never a good idea to be a bigoted, narrow-minded, backwoods, illogical, immoral, animalistic, reckless person. After all, it's the 21st century. I thought the societal norm was to treat humans like humans. I thought the mantra of the day was, "I believe in science." Science is not your friend if you are a pro-choicer. Neither is philosophy. Neither is truth.
 Peter Singer, Practical Ethics, 2nd ed., Cambridge: Cambridge University Press, 1993, pp.85-86
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 Steven Schwarz, The Moral Question of Abortion (Chicago: Loyola University Press, 1990), pp. 15-19