In the wake of the success of Proposition 8 in California, this has appeared in several blogs (mostly on LiveJournal):
Copy this sentence into your journal if you have ever been in a heterosexual marriage and the idea of same-sex marriage being a threat to your heterosexual marriage is the biggest bunch of shit you ever heard.
I'm not sure I can quite affirm that, just because there's such a tremendous amount of stupidity and silliness out there, but it's certainly a strong contender.
I have long thought that issues like love and sex and religion and fertility are basically none of the state's business, and that its involvement in "marriage" should amount only to having some sort of legally recognized partnership (which might or might not be called "marriage") that people – any people – can enter into, whereby they pool their goods and various other interests. Then those who want the partnership they're entering into to be formally approved by their religion, or marked with special declarations of love and faithfulness, or whatever, can do that in whatever way they find best. (And those who feel that their own marriage is somehow threatened by someone else's can go jump in a lake.)
And, in case it's not obvious, such a partnership needn't have anything to do with love or sex or children, though of course many of them would.
This is a special case of a general principle that seems obvious to me (though I have trouble saying exactly why it should be right, which may be a warning sign): governments shouldn't try to legislate for things they can't reasonably enforce – such as a partnership's really being anything to do with love, sex and children.
(Of course there are all sorts of details that would need to be right, and I'm not going to try to discuss them here.)