I'm not sure I can offer any new insights, but I'd like to chime in, anyway.
I, like most of the "no to gay marriage" faction, do not care what consenting adults do in privacy. At all. I fully accept "their" absolute, inalienable, Constitutionally protected (see Am 9, and Am 10) right to engage in such behavior. I don't approve of it, but my approval is not germaine to the question of rights. No advertising, media blitz, popular culture icon, or pithy quote will convince me that homosexual behavior is okay, by whatever definition one assigns to "okay". Okay?
If an employer only extends benefits to straight couples, so be it. Employers have rights as well. If Company A denies insurance bennies to same-sex couples, so be it. If same-sex couples (hereafter: SSC) think that Company A is behaving "wrongly", then let the SSC's draw the public's attention to Company A policies. Let the marketplace decide whether a "homo-antagonistic" company survives in the marketplace. I also think employers should be free to discriminate (in the classic sense of the word) against anyone they choose, as far as employment is concerned. With sufficient exposure of this practice, and with a sufficiently free market in employment, either the company changes, dies, or prospers.
All that being said, other than employee benefit issues, what measurable, tangible benefit do SSC's receive from calling their relationship a "marriage"?