I have to disagree with you. Societies chose to protect and promote that which is beneficial to the society and rightfully so. Every law is in some form or another “social engineering” and unavoidable. We try to engineer our society to meet our moral standard of justice, and that includes any consequences of marriage or is dissolution.
As for “civil unions,” these promise no benefit to society and deserve no special consideration. Nothing is stopping anyone from contracting to live with one or more people. It isn’t a marriage and it deserves consideration than a contract to rent an apartment.
The issue however, which we must not lose sight of, is the usurpation of power by the Supreme Court. You have fallen for the distraction, arguing marriage versus contracts which is exactly what the philosopher king criminals want you to do. It spares them from a mob with tar, feathers, rails and ropes.
The governments job is to provide infrastructure and defense and that’s it. It’s societies obligation to shape society. Let’s leave the state out of it.