Law, Democracy, Social Consensus and Marrying Your Cousin
When I pointed out to Jack that Posner had nicely taken us to task on this matter in the new book, he replied that many people simply find our view untenable because they hold that there clearly exists social consensus on numerous broad political and ethical issues - especially prohibitions against, say, incest and murder. I will speak for myself here (Jack may or may not agree) but whatever consensus might exist on such matters exists at such a level of generality as to render it more or less useless as a means of making or deciding law. And any 'social consensus' at less abstract levels is more than likely the accretion of imposed 'values' and 'commitments' and so might more accurately be depicted as social acquiescence in the face of long-standing asymmetries of power. (Posner offers the example of the ways contract law is suffused by capitalist values which may be true enough, but there are plenty of people in our heterogeneous society who actively resist and dissent from any consensus around such values.)
As for consensus itself, I would point out that there have, in the past, been equally certain sorts of consensus - mostly concerning the practices we construct around surrounding Elliot's triad of "birth, copulation and death" - that now strike us not just as absurd but as racist, sexist, or both. Think of inter-racial marriage and variety of miscegenation laws. Think of the myriad repressive laws against homosexuality. Can 'social consensus' justify the cruelties and injustice meted out in those domains? Does it count as anything beyond a rationalization of bigotry?
So, what about marrying your cousin? It appears (and here I thank the kind folks at 3 Quarks Daily for their post on the subject) the consensus - social and legal - against it is roughly as ill-founded as those that once rationalized miscegenation laws. As the authors of one study argue, laws against marrying one's cousins "reflect once-prevailing prejudices about immigrants and the rural poor and oversimplified views of heredity, and they are inconsistent with our acceptance of reproductive behaviors that are much riskier to offspring. They should be repealed . . . because neither the scientific nor social assumptions that informed them are any longer defensible." The problem, on this account, is political. And while I have no interest in marrying my cousins nor they me (I've proven a poor bet in the marrying game) I see no reason to have laws against it.
* Richard Posner. 2008. How Judges Think. Harvard UP.
** See, among other places, Jack Knight & James Johnson. 1996. "Political Consequences of Pragmatism," Political Theory 24::68-96 and Knight & Johnson. 2007 "The Priority of Democracy," American Political Science Review 101:47-62.