Here is my take on what is at stake:
Marriage is above all a social institution, above and beyond, that is, a merely personal arrangement. This idea was impressed on me by contemplation of a strange and superfically trivial circumstance. When reading Rabelais' Gargantua, I found a humorous account of how a "bum-baliff" is beaten half to death at a wedding under the guise of "exchanging blows". Did you you ever, when you were younger, exchange perhaps-not-so-playful punches to the shoulder as a form of greeting? As Rabelais alludes, this is a hoary peasant tradition. Being illiterate, these punches would be exchanged literally to "impress" the memory of the occasion on the community. The wedding, as the establishment of a new family unit, was in this way acknowledged by all, and the couple was in their turn reminded of their important role by the community festival held in their honor.
I have felt that wedding receptions continue to fulfil this role, even absent the exchange of blows, and I have felt a sense of betrayal when, as has happened, the couple so honored has split up within months.
This brings us to the problem of "the death of marriage". This court ruling in favor of "gay marriage", is only possible because we have already lost the sense of importance of marriage as a social institution, and in fact society has largely already been restructured along totalitarian lines.
"Bear with me, my heart is in the coffin there with Caesar ..."
Too bad I can't "compliment" you (Gargantua-style), but that was a great description of what marriage is.