The fact of the matter is, no matter what the law says, two men or two women cannot get married.
Whatever their relationship is, it isn't marriage, and legalizing same-sex "marriage" is simply the same as calling a dog's tail a leg.
In point of fact, the best they can have is some sort of "civil union," a legal arrangement that provides some benefits, but that does not really transcend its status as a legal entity (not, mind you, that I am in favor of civil unions, but they are not as definitionally absurd as same-sex "marriage").
What legalizing same-sex "marriage" ultimately will do is to pull down opposite sex marriage (read real marriage) down to the level of civil union.
That is the true reason to oppose same-sex "marriage." By its very naturre it redefines marriage and removes the transcenent element to it.
Reading back through my archives, I find out that this is not the first time I've made this argument, but I still think that it bears repeating.
That is all.