As I've often said, the distinction between sacramental and legal marriage is a vital one to maintain or, it often seems in America, to create. The First Amendment exists for a reason and cuts both ways; I doubt you'll find many Christians who genuinely want congressmen and/or legislators legally defining sacraments. As you note, many kinds of civil unions already legally recognized as marriage will never be recognized as such by most churches, so one more is rather trivial. Monopolizing the term "catholic" may, however, be an anti-trust violation.