How about I follow the rules of my Christian Lord and you follow whatever suits YOU. Don’t impose yours on me and I will likewise refrain. Ok?
OK, so you want to eliminate marriage by simply making it whatever anyone wants to call it, no definition whatsoever.
People can already do that of course, and always could, it just wasn’t legal, so what is your complaint, you want it to be the law?
Also how do humans suddenly live with no such thing as legal marriage? (Legal) marriage has always been defined by a legal authority, whether government law, the state church, or tribal law or whatever.