On reflection, the anatomical point is probably invalid - trying to get a conclusion in the imperative mood from premises in the indicative mood, or, in short, an "ought" from an "is". (Hume's law.) Nevertheless, altering the definition of marriage that has been around for millennia seems a bit reckless. What's wrong with marriage for heteros and civil partnership for homos? There's nothing necessarily second-best about civil partnerships, and if civil partners want to regard themselves as husband and husband, or wife and wife, no-one's stopping them.
And that is my last word on the subject. If some posters still regard me as homophobic, fuck 'em.