As you know, I'm pretty much in agreement with with Muon, though I'd call it the "actuarial argument." That does effect me, and all you that do/will get pension funds/Social Security.
Now, I'll tell you what deal I'll offer to all proponents of gay marriage/civil unions. I'll start favoring full benefits for same sex marriages provided you make it illegal for a surviving spouse to get pension benefits, from this point onward. The only it will be legal will be if decedent specifically paid in more to cover the costs; single, unattached people (me) don't pay anything.
In other words, when Dad/Gandpa dies, you better be prepared to fully support Mom/Grandma, personally. If you don't, they starve to death.
Any takers?
I take it you favour making it illegal for the surving spouse in current marriages to get pension benefits? Surely 'sham' arrangements are prevailant in heterosexual marriage too.