The thing people tend to not understand on this issue is that voters change opinion faster than legislation can catch up, much faster than legislation can catch up. And you really only have so many die-hards on either side where this is an important issue for them. Many people couldn't care less if people of the same sex are allowed to marry because they feel it doesn't affect them whether they are or aren't.
"A woman is like a teabag, you never know how strong she is until she gets in hot water." - Eleanor Roosevelt
Keep your religion out of other people's marriages.
I would think libertarians would be for expanding the rights of all and not allowing some folks to try and restrict the rights of a few from enjoying full equality.
I don't want to marry a Dude, I picked a female to go through life with. That said I don't see who has the 'right' to tell consenting adults they can fight for the country but not all the blessings some go on and on about...