How does one approach a contentious, emotional issue such as abortion from the perspective of meta-ethical subjective relativism?
Some people are ethically offended by abortion to the same degree as I'm ethically offended by the murder of any born person. Some people, such as myself, are not at all ethically offended by abortion itself. I really don't care one way or the other: Have as many or as few abortions as you please. What offends me ethically is interfering with the mother's autonomy.
The fundamental principle of meta-ethical subjective relativism states that there is no matter of objective truth to either position. If abortion offends you more than interfering with the mother's autonomy—or vice-versa—that's just a fact about your consciousness. In just the same way, if murdering random people on the street offends you more than interfering with the autonomy of the murderer—or vice-versa—that's just a fact of your consciousness. Science can undermine specious rationalizations (no, a six-week-old embryo does not experience any sort of pain or pleasure) but it can't settle the fundamental question objectively, by appealing to real properties of real objects.
Now, it's determinably true that murdering people on the street offends almost everyone, hence it's unsurprising that laws against doing so are uncontroversially accepted. However, it's determinably true that abortion does not offend almost everyone; worse yet, any law permitting or prohibiting abortion will deeply offend half the population. We can't just take a vote and go with the majority; the issue is too emotional, too important for such a simple measure. It's not a matter of raising the sales tax half a cent to pay for a new baseball stadium.
We could, of course, pick up guns and start shooting. At some point, most everyone left alive will have the same attitude (and the rest will pretend pretty hard), and we can go back to the preponderance of opinion. This is not a particularly efficient method of resolving controversy, but we do sometimes have to resort to it. That's how, for instance, we answered the controversial questions: Should Germany rule Europe and Japan rule Asia? But we'd like to find a way to resolve these questions without killing a lot of people.
One method we can address these sorts of questions is by "raising" the level of abstraction until we can find a principle that most people agree to and that most people agree to apply to the direct issue. This is the method that we use to address controversial questions such as what religion to profess, what opinions to write and publish, whether or not to allow the police into a private residence, etc. I may have to grit my teeth at Ann Coulter, but my desire to put her in jail for her horrible, offensive opinions is outweighed by my desire for the abstract notion of freedom of speech.
So what abstract principles can we consider to control the issue of abortion? The pro-choice side has several good principles: principally medical privacy and the higher value of the mother's sapience vs. the embryo's non-sentience. These are all good principles; moreover, they're principles I think should be universal (applying in all cases); I agree with these principle regarding abortion as well as all cases other than abortion. To prohibit abortion would violate these principles, which I don't want.
But, of course, I really don't care much about embryos anyway, so my position is biased. What about the principles the pro-life side promulgates?
The stated principle is, of course, that an embryo is unequivocally human, and we should protect all human life: To kill an embryo is then the ethical equivalent of killing any human being. This is not an entirely bad principle, but does it hold up as a universal principle?
One argument is that it's simply more consistent and "simple" to protect all human life, the so-called "seamless garment of life." But this position, when examined closely, is not particularly consistent or simple, being filled with arbitrary boundaries: It's more of a ragged, patchwork garment. I tend to value human life, but not absolutely: I have no problem with self-defense nor with voluntary euthanasia, and, while I'm opposed to the death penalty, I just can't get too worked up about executing a guy such as Timothy McVeigh. (Note that it's a fallacy to argue that if you permit the killing of some human beings, you must therefore permit the killing of any human being, as if all our moral beliefs must be reducible to a single principle.)
I also have to ask: Is this "human life" principle actually sincere, or is it disingenuous? For some, of course, it's completely sincere, but is it sincere for everyone, or even most everyone? One strong counterargument comes from the popularity of rape and incest exceptions. It would be a fallacy of reduction to argue that permitting the killing a rape-generated fetus entails permitting the killing of a rape-generated born child, but even so, the notion that some particular kinds of sexual relations would render the resulting entity non-human (or render a human being outside the protection of law) seems bizarrely counterintuitive.
Another strong counterargument is that most (but again, not all; I'm dealing in generalizations here, not universals) pro-life proponents are either strongly against—or only tepidly for—easily accessible birth control. You do not typically see anti-abortion protesters handing out condoms outside the clinic.
Applying the scientific method in a sociological sense, the simplest explanation that accounts for all of these phenomena is that the pro-life position is (in general) strongly influenced by the principle that consensual non-procreative sex is wrong, and that women should suffer the natural consequences of their wrong acts by bearing the baby to term. I simply cannot support this principle: I wholeheartedly approve of people having all the consensual, non-procreative sex they want.
I'm convinced that if you removed this misogynist and anti-sex plank, the pro-life movement would collapse. You can't even pass an anti-abortion law in South Dakota without a rape and incest exception. I'm equally convinced the pro-life movement would collapse if this plank were made explicit and taken to its logical conclusion: legal prohibition not only of abortion but also homosexual, premarital and extra-marital sex, even perhaps prohibition of birth control and non-procreative martial sex.
The whole controversy is being sustained on lies and bullshit. Just add the values of honesty and sincerity, and it's easy to find a level of abstraction that we can all agree on.