Just another false alarm...

Tomorrow is the day when same-sex couples will be able to register for civil partnership in England for the first time (with the first ceremonies happening on the 21st December). Under the terms of the Civil Partnership Act 2004, certain groups of people aren't allowed to become partners. The prohibitions listed are pretty much the same as for marriage, so that you can't get partnershipped to your (adoptive) child, (adoptive) parent, grandparent, grandchild, sibling, half-sibling, parent's sibling or sibling's child. All the prohibitions are listed here.

Leaving aside the parental and grandparental relationships, where there are pretty good arguments to be made concerning power differences and all that sort of thing, I wonder what justification there can be for forbidding sibling incest in civil partnerships. I'm assuming here that 'it's disgusting' isn't a good enough basis for legal prohibition, and wouldn't be even if every single person in the country thought this.

The issue's murky enough when it comes to heterosexual incest, since it seems easy enough to avoid, or at least calculate, the risk of birth defects in the offspring of incestuous relationships. But when there's no question (at least with present technology) of the relationship producing offspring, as with gay couples, what argument can there be for prohibition, other than a misguided notion of equality with heterosexuals - equality which gays aren't really being granted anyway?