After a bit of nudging from LGBT friends, and some kind words from over at American Mercenary, I'll cave in and answer "Well, what do you think should be done?" regarding the same sex marriage debate rather than "How not to achieve it?"
To do the issue justice, over the centuries, marriage and marriage-like relationships have performed a veritable legal drag show, appearing in different and evolving guises over the years. We need only look at the anti-miscegenation laws (inter-racial marriage/relationships) passed and repealed in our own country, the rise and fall of Mormon polygamy (still a subject for occasional debate and police raids), arranged marriages (and the more familiar corollary in this country, the requirement of the brides fathers or eldest living male relatives consent) to realize that even this tiny subset of changes hints at the vaster changes in the institution in North America, Europe, and beyond.
Things have, for instance, changed since the days when excessive affection between spouses (in private, even) was considered poor form, and protestant preachers railed against affectionate "pet" names and familiarity between spouses, lest it undermine the husbands authority.
I will leave it for another time, but ample evidence exists that in at various times and places over history that, indeed, same sex marriage (or things so oddly similar as to beggar other explanation) has existed without the world ending, or societies dissolving in response.
That said, however, where do we go from here?
Ever hear of that old phrase, "Everything old is new again?"
I suggest that marriage as we know it today has three separate functional pieces or jobs -
1) A religious ceremony.
2) An established relationship structure with specific and broad rights and responsibilities and organized default entry and exit strategies.
3) A familial element, the notion of caring for minors (pre-existing or appearing on scene after the marriage commences) and in the longer term, the partners caring for each other in their old age and thus reducing the burden of the aging upon the taxpayer even as the aging partners independence and experience are preserved and enhanced (ideally).
Again, the wild-eyed libertarian that I am, I favor a minimum of state intrusion. If only for the sake of keeping the bloodshed from spontaneous techniques to a minimum, I favor at an absolute minimum some kind of "this is how you break up without emulating Henry VIII or variations thereupon" kind of mechanism - the whole "judge as mediator/arbitrator" thing has a whole bunch of good things going for it, not least among them the aforementioned faint vague hope of keeping the bloodshed to a minimum.
I favor the notion of divorcing the civil and societal elements (i.e., all the legal privileges, obligations, benefits, etc.) from the religious element. In other words, under this scheme any church (and no, you don't get to draw me into the red herring of defining who's a church and who isn't) can perform - or refuse to perform - any little old wedding ceremony between competent and consenting adults that thrills their little hearts...such ceremony will simply be wholly irrelevant (not unlike a funeral) to the legal system.
The flip side of this is that suddenly the *civil* variety of marriage is the only one recognized by the courts and is available to all competent and consenting adults outside of a reasonable degree of consanguinity and, perhaps, a pre-marital requirement of "full disclosure" of any pre-existing health conditions between the parties to the grand event.
Anyway, that approach probably makes far too much sense for it to ever to occur.