Compare Utah Rep. Jason Chaffetz's pro-family reasoning, quoted by Jon below, to that of Sen. Jeff Sessions. Chaffetz can't abide giving committed same-sex couples who work for the federal government equal employment benefits because the proposal doesn't include unmarried straight couples. In contrast, Sen. Sessions predicts the demise of Rep. Mike Honda's bill to provide recognition to the noncitizen partner in committed same-sex relationships (the recognition immigration law now automatically grants to a heterosexual spouse) because it "would be creating a special preference and benefit for a category of immigrants based on a relationship that's not recognized by federal law and overwhelmingly by most states."
So Sen. Sessions views gay equality as a "special preference" while Chaffetz doesn't see gay equality at all, only straight equality.
Let's review the bidding, then. Same-sex couples can't have their relationships recognized by the federal government because of DOMA, and shouldn't be asking for any "special" rights, such as treatment equal (or even roughly equal) to what heterosexuals expect. And if gays do ask for any benefits for their relationships, heterosexuals should expect, not only the benefits they now recieve for being married, but benefits for not being married, so that they'll be treated equally to a group that any reasonable person can see are now treated unequally.
All of this arises because of the GOP's fundamental inability to aknowledge that same-sex couples are not treated equally, or fairly, under current federal law. That increasingly obvious blind spot leads to all of their incoherence.