Found this piece this morning on Proposition 8 and the Right to Marry. Short and sweet and I disagree entirely. Yes, you would have trouble justifying giving benefits to unmarried same-sex couples if they had the option of federal marriage. Until then, it addresses an inequity. Whether you can just give blanket benefits to any partner, or any adult named by an employee, is more an issue of cost.
Everyone I have ever heard discuss the idea of allowing everyone to designate one person to receive their benefits immediately starts coming up with exceptions. What about the person who has two living parents who need care? What if a person has more than one adult child in need of care? How can you limit it to one? But if you don't, you are right back at unequal treatment. Those with the most dependents get the most benefit from their job, which is hardly equal pay for equal work.
U.S. Foreign Service employees seek benefits for their heterosexual partners - lawsuit may challenge State Department's lack of equal treatment
Law professor Nancy Polikoff is author of Beyond (Straight and Gay) Marriage: Valuing All Families Under the Law. In the introduction to her book, she says that couples should "never have to marry to reap specific and unique legal benefits." This article suggests that as employers extend limited benefits to same-sex partners of employees, they face the problem of justifying restriction of these benefits on the basis of sexual orientation. One heterosexual couple has threatened to sue the State Department for discrimination over restricting its extension of benefits to same-sex partners of Foreign Service officers.