“This is the fruit of the heresy which teaches that marriage is a contract when it is actually a sacrament.”
Nailed it. To the state, it is simply a piece of paper denoting a contract that carries benefits and strictures that can be broken and resumed between any parties that judges, pols, or the majority decide should have them. And that’s it. Pope Leo XIII warned about it 130 years ago.
Freegards
Treading on theological ground here, but I'm not sure that marriage is a Sacrament at all, because a Sacrament is when the Word is joined to a material object for the explicit purpose of delivering God's grace and forgiveness of sins.
Having said that, marriage is definitely an institution ordained by the Lord in the first place. We can't treat it as a contract or as a tradition--it has been instituted by the Almighty for our good, and we do the Lord and ourselves a great disservice by pretending that it is anything but divine in nature.