I didn't get any takers here, but Ryan Anderson takes a crack over at First Things at the question I asked in the wake of the WHO-Guttmacher Study. As I read his thoughtful post, he suggests that a consequentialist approach to the decision whether "there ought'a be a law" may not be appropriate or decisive in all moral contexts, or, perhaps, consequentialist considerations are muted in certain contexts. His post provides a lot of food for thought.
I do have a question, though, about a passing analogy he makes to slavery. Anderson asks:
What if during the early days of abolition people claimed that the results of outlawing the slave trade wouldn’t reduce the number of slaves but would only have deleterious effects on those slaves who now would be transported on the black market? I doubt that any of us would consider this a reason not to start down the road of criminalizing slavery and emancipating slaves.
I'm not sure I fully buy the analogy here. Slavery is, at least in substantial part, a legal (status) relationship. As such, a law outlawing slavery would, in some substantive sense, be guaranteed to be effective in that it would immediately transform the legal status of the former slaves. Now, Anderson is right of course that such a law might drive relations of involuntary servitude underground or might simply lead slavery to be replaced by new legal institutions (e.g., debt peonage) that make former slaves even worse off in some respect, or perhaps no better off (although this is certainly contestable, since one might plausibly argue that even the most destitute and dependent free person is better off than the legally enslaved). The analogous question to the one I asked would be whether these
consequences would be worth paying for the abolition of legal slavery. (As an aside, at least one feature of abortion makes me think it would to be
harder to stamp out than slavery, and that is that, unlike slavery, all
parties involved (with the exception of the fetus, who cannot speak for
him or herself) consent to the procedure. As with other consensual vices --
prostitution and drug sales spring to mind -- this dimension might make
enforcement of laws prohibiting abortion very challenging in a free
society.) I think the ultimate answer would depend, at least in part, on whether we thought the hypothetical consequences of outlawing slavery were really beyond our control, but I'm not sure it's absurd to suggest that they would be at least relevant to the question whether (or perhaps how) to abolish slavery.
For a different take on this question than Anderson's, take a look at this post over at Catholic blog Vox Nova.