What do you make of the distinction between “marriage” (religious) and “civil union” (legal)? That would at least seem to accomodate the fact that the government (or, ideally, other institutions filling its current role in keeping the peace and settling disputes) has a different role than religion (specifically, that the former has obligations to be just and evenhanded that are not binding on the latter).
It’s not so much what I believe that’s at issue but what those with the agenda of extending marriage to same-sex couples wish to accomplish. California already had domestic partnership laws on its books when they pushed for the redefinition of marriage to include same-sex couples. The agenda to norm the acceptance of same-sex coupling won’t stop at the government marriage license bureau but is being pursued as vigorously toward acceptance on the church altar.