Benefits for straight married couples make no more sense than benefits for homosexual couples do. Because deciding to cohabitate with a person of the opposite sex, procreate, all that -- well, it's a lifestyle choice. Those people who argue that being straight is pure biology, like being black or white, need to wake up and smell the pheromones.
Nobody makes you act on your urges, whatever they are -- heterosexual or homosexual. And yet straight people seem to think they deserve some sort of compensation for giving into their urges while denying people with differing urges the same compensation. Deny them all, I say. Let everybody fend for themselves, and let the chips fall where they may.
Given all the people who think that that homosexuality is purely a personal choice, I must conclude that giving into any physical urge must be an anomaly. Therefore, a life of pure abstinence is the only natural choice for the human who wants to live his/her life to the fullest. Don't have sex with the same sex if you want to. Don't have sex with the opposite if you want to. Don't eat. Hell, don't even breathe. Those are all physical urges. You must deny them.
Where do we draw the line? It might be easier and more beneficial to a free society to give people the freedom to make their own choices. And if we don't support compensation for some of those choices (the dirty sex ones) then why support them for all the dirty sex ones? After all, there's only a couple of inches between sticking a penis into a vagina and sticking it into an asshole. And we've ripped the country apart over those couple of inches.
Don't give the homos any rights based on their sexuality. This is fine with me. But stop giving heteros rights, too. To hell with all you weak specimens who can't control your physical urges.