Originally Posted by MS Fowler

Marriage is, or has been BOTH a legal contract AND an "institution".
I have no issue from the legal contract side of the issue; you made that argument well.
Its from the " institution" side that I have some conflict. I haven't checked, but I would tend to think that "institution" is religious language reflecting the historical and biblical understanding that marriage was instituted by the Creator. It would therefore be a holdover from when governments were involved in religious affairs. Perhaps we need a clearer distinction between the state marriage and the religious one. Since the laws have been written the way they were, "marriage" is the term that is used to convey the whole list of rights you listed. I see no practical way to unwind the way the term has both a civil and a religious meaning.
So we have civil marriage performed by a state-licensed officiate, and a religious ceremony performed by a licensed minister; sometimes the same "officiate" fulfills both roles.
As much as I desire to preserve the term "marriage" for the religious ceremony only, I see no practical means to do that in out pluralistic society.