Anyway, Logan tackles the question of the day from a slightly different Francophone angle: not 'equality' but 'liberty'. I think he puts my concerns in a helpful way: marriage is marriage. Some parts of it can be altered, and need regulation (registration, dealing with dissolution), and the State has an appropriate role in the rules regarding such. But the State defining the essence of marriage (strictly speaking, 'redefining') is new territory in the history of humanity.
"Well, some French friends put the notion of equality under examination. They say same-sex marriage "n'est pas l'egalite, il s'agit de la liberte". It's not about equality; it's about liberty.
The whole argument is here.