Politics is the art of the possible: extending marriage benefits to gays and lesbians is a lot easier than clawing it away from all straight couples in order to satisfy a desire for libertarian ideological BS.
But then, this was never really about benefits in the first place. If it was, they could have had civil unions a decade ago. This is about getting the Government to endorse it as Marriage to stuff it in the face of all the homophobes out there. This has always been entirely about ideological "BS", but not the kind the myself and any other libertarians are spewing.
And stuffing a few homophobes is good. They have been persecuting LGBT people for millennia so fair turnabout.
On the other hand, we have people being harmed by the unreasonable jank thrown at homosexuals who wish to marry. The perfect must not be made the enemy of the good out of a sense of ideological purity.
The thing about Government power, though - everything seems all nice and cool when it's pointed in a direction that you like, and it makes everything happen real fast and lays the smack down on your ideological opponents. But that power can turn on a dime and get pointed right back at your side, as has happened a great many times in history. Think it can't happen here? I hope it never does, but it does have a nasty tendency to happen in places and to people where they thought it couldn't, where they keep on doing the simple and efficient thing, because that couldn't possibly ever happen to us, right?
Meanwhile, my/our camp of libertarians saying hey, the Government really shouldn't be in the business of deciding who can be in what sort of relationship with who else or blessing either side of a controversial argument is disappointingly small and quiet and usually ignored.