Here, for those who read French, is the Chief Rabbi’s site containing the open letter to which Benedicts Christmas address referred. Those who don’t read French might want to revisit the Thirteen Theses .
A sample: Que lon ait lune ou lautre des visions du monde, on voit bien que ce qui se joue derrière « le mariage pour tous », cest une substitution : une institution chargée juridiquement, culturellement et symboliquement serait ainsi remplacée par un objet juridique asexué, sapant les fondements des individus et de la famille. (“Whether one has the one world view or the other, it is quite clear that the intention behind the slogan marriage for everyone is a substitution: a juridically, culturally and symbolically charged institution is to be replaced by an asexual juridical construct, undermining the foundations of individuals and of the family.”)
One thing this essay helps to demonstrate is the foolishness, if not the dishonesty, of the notion that support for same-sex marriage is support for what is natural, whereas opposition to same-sex marriage is mere bias against forms of nature different than one’s own.