Sure we're gay
Two elderly British sisters want to be treated as lesbians in civil union, for tax purposes. And I say: why not? I suspect it would be easier for them to simply declare themselves gay and get "married". But there's probably a law against gay siblings getting "married", even though there's no compelling State interest for such a law; after all, it's not like they're going to reproduce. They'd doubtless find such a union "quite improper", but hey, they're old ladies; they can get away with being a bit dotty. And there are folks who would say, "Oh how sweet! It's just like 'gay until graduation': queer until the bier."
These ladies are demonstrating the absurdity of the law. I've been using those scare quotes because the State can't marry gays, for the same reason it can't marry straights: it's not part of a valid apostolic succession, and thus is not able to administer the Sacraments. We're all domestic partners. And what is the State's interest, and the individual's interest, in domestic partnership? If it's security for children, then there's no point in gay "marriage" unless there's already a child, either naturally or by adoption. And if it's about children, wouldn't "one of each" be preferable? If it's about sex, do you want the government to have an interest in your conjugal relations? Just as we don't need a state licence to screw, having a state licence is no proof that we are actually getting any.
No, "marriage" is primarily about estate planning, and certain economic rights and obligations. That being the case, why bring sex into it at all? "Marry" your gay lover, "marry" your sister, "marry" your adult child; I don't care. If the state shouldn't discriminate against homosexuals, why should it discriminate against asexuals?

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