Glenn Reynolds links to a discussion of marriage by cousins. William Saletan is for it while Megan McArdle disapproves.
The fact is that the legalization homosexual marriage cannot be the end of the re-definition of what a marriage is. Once the ages-old definition of marriage as between a men and a woman is no longer valid, other barriers need to be broken to avoid charges of discrimination.
And everyone knows, discrimination is not allowed.
The weak excuse that cousins marrying could cause heightened chance birth defects is ludicrous. So what? Homosexual unions cannot lead to children at all while certain homosexual practices lead to the high probability of deadly diseases like HIV. Those appear to be no longer valid reasons to restrict either marriage or non-marital homosexual practices. The mere though is met with accusations of homophobia.
Perhaps we will have to create new words for practices that are now forbidden but should not be by reason of legal symmetry. What should we call the fear of marriage by cousins? “Cousinphobia?” And then there are those other fears expressed by the backward “bitter clingers” like "Polyphobia" (the groundless fear of multiple wives or husbands), or “Speciesphobia” defined as the fear that some girl will want to marry the horse that she loves.
And then there is the well known “Inanimateobjectphobia.” But that’s a few years down the road.