Abortion is morally wrong

[Angrboda]

I think a lot of red herrings are being thrown around because people disagree with the conclusion of Arthur's argument, but can't find any substantial point of attack from which to refute it. People are flailing around, attempting to hit the argument, and coming up with nothing but air.

Is morality subjective? Objective? Who really knows? Whether you agree that morality is objective or not, in most modern societies, it is agreed that it is wrong to kill an innocent human being (without justification), at least in the case of those already born. So, excepting justification for setting the general rule aside in particular cases, the rule is on the whole endorsed by modern societies, whether it was arrived at objectively or subjectively. The question then becomes whether the rule is being used correctly in his argument or not? So far, I don't think anybody has pointed to a clear flaw in his application of the rule. (Not saying there aren't flaws, just that nobody has hit upon any of them yet.)

As for the burden of proof question, from his statements, it appears that Arthur is appealing to an epistemological framework invented by the philosopher Stephen Toulmin. This is an alternative way of evaluating debates and arguments from the burden of proof framework being insisted upon. I'm relatively confident that few here are familiar with Toulmin's framework, but it is a legitimate epistemological standard which, while not unanimously endorsed, has wide acceptance in a broad range of fields. You may or may not find Toulmin's framework appealing, but he's not simply pulling something out of his ass and ignoring burden of proof.

My motus ponens is as follows:
1. It is morally impermissible to kill an innocent human being
2. A fetus is an innocent human being
3. Ergo, it is morally impermissible to kill a fetus.

In the general case, it may be true that killing an innocent human being is wrong, at least as it applies to the case of born human beings, as the rule is generally conceived. However, any rule which is true within a given domain (the already born) can be made unsound if it is applied beyond the domain in which it is defined. You have, by your definition of genetic completeness, extended the domain over which the rule is normally applied to include the preborn. If this application were uncontroversial that would be one thing, but it is not. There are many who do not agree that the preborn qualify as a human being, and others who think that, even if the preborn is human, the general rule does not apply to them. So the general rule, when applied to the already born, is uncontroversial and widely accepted. However, you've extended the general rule to a novel domain, and it's not altogether clear that the general rule is sound when it is extended to this specific application. If I accept your extension of the definition of human being, and by implication, your extension of the general rule into this new domain, it is not clear that the specific application of the rule to the preborn is sound. Since you, by definition, have extended the typical domain of the general rule, and the general rule includes this specific application of it, doubt about the soundness of the general rule follows from its inclusion of this specific case. You might say that doubt about the specific case 'infects' the general rule. So by extending the domain of application, you've put the general rule in doubt. So you are appealing to a general rule to justify the specific case, but the specific case depends for its justification on the soundness of the general rule [across all domains] which you've put in doubt by extending it to this specific case. As such, appealing to the soundness of the general rule to justify the soundness of the specific case, when the soundness of the general rule has been put in doubt by your definitional extension is an example of circular reasoning. The soundness of the general rule is used to justify the soundness of the specific rule, but the soundness of the specific rule affects the justification of the general rule. By appealing to the general rule in this way, when your very argument itself as read puts the general rule in doubt, amounts to a form of begging the question. The same would occur if I were to extend the definition of 'person' to include chickens and cows; it would be unclear whether the general proscription against killing innocent persons still held. I cannot restore order to the rule by deriving my justification from the general rule because that which I seek to justify has put the general rule itself in doubt. That would be a case of begging the question as well.