The argument that gay marriage would subtly undermine the unique legitimacy of straight marriage is based upon a fallacy. For heterosexuals, straight marriage would remain the most significant–and only legal social bond. Gay marriage could only delegitimize straight marriage if it were a real alternative to it, and this is clearly not true. To put it bluntly, there’s precious little evidence that straights could be persuaded by any law to have sex with–let alone marry–someone of their own sex. The only possible effect of this sort would be to persuade gay men and women who force themselves into heterosexual marriage (often at appalling cost to themselves and their families) to find a focus for their family instincts in a more personally positive environment. But this is clearly a plus, not a minus: gay marriage could both avoid a lot of tortured families and create the possibility for many happier ones. It is not, in short, a denial of family values. It’s an extension of them.”
— An excerpt from Andrew Sullivan‘s landmark 1989 essay, “Here Comes the Groom: A (Conservative) Case for Gay Marriage” for The New Republic, recently reprinted by Slate.