If you look at marriage as a legal contract, then there's absolutely no benefit that a marriage conveys, that can't be obtained legally with a little forethought (wills, "next of kin", inheritance, etc).
If you look at marriage as a religious contract (as I do) then...unless you are arrogant enough to re-write God's word, then there's nothing in the Bible that says "Marriage is between a Man and a Woman, unless you happen to disagree with that." End of story, as far as I'm concerned.
So, IMHO, all this boils down to is gays bellowing at the top of their lungs that "They're just like us, except different."
"Show me just what Mohammed brought that was new, and there you will find things only evil and inhuman, such as his command to spread by the sword the faith he preached." - Manuel II Palelologus
I would almost agree that civil unions would be the answer ... or having government get out of the marriage business entirely.
Except for one thing: forcing priests/ministers and organized religion to marry them is the next logical step on the campaign.