Why do you need a theological argument? "The church should treat all human beings with dignity, respect, and equality," should be sufficient. Who cares how that line of thinking descends through the centuries?
My feelings exactly. Sometimes things don't need to be viewed through a theological lens; they are what they are. If you see two men or two women who are everything to each other you don't have to peel it back and analyse it's worth, morality or integrity. It doesn't need to be complicated.
Surely someone who's spent a good chunk of their life arguing against "The Bible says so" ought to appreciate that a "just so" argument doesn't hold any water. This sort of view reduces the pro gay marriage view to nothing but sentiment.
We ought to have a sound basis for our morality if we want to convince others. No matter how obvious something might be to one person, someone else might have a totally different inclination.
I think afleitch means that some things are just morally neutral. Gay marriage proponents aren't arguing that gay marriage should be legal because it's moral, but simply because it isn't immoral, at least in an objective sense.