This is childish, every law has a moral component, every single one.
And as for And why, if you are hell bent on redefining marriage, would you limit it to two members of the same sex who engage in homosexual acts? I have never known heterosexuals to engage in homosexual acts, so I don't know what you're getting at.
What I am getting at is quite simple, if you want to extend marital privileges to two homosexuals then you have to extend them to any two or more people who wish to enter in a union be it sexual, celibate or platonic. Otherwise, you are simply drawing the "Correct Behavior" line a bit further down the road than us evil social conservatives.