Really, as has been said, if you're straight, why would you give two tosses about who someone else marries?! What business is it of yours?
My father once said in this vein, Well, them marrying puts a blemish on those of us who marry as it should be: a man and a woman.
I love my dad, but what a simpleton dumbass.
Religion is for weak, dumb people and marriage is for those who fail to listen to intelligent warning.
If two dudes wanna hitch it up, go for it. Have a ball.