I disagree, Jenn.
I am 100% atheist, and I consider myself 100% married.
Marriage is a social institution that is found in every culture around the world, and it takes many different forms.
Marriage is a social institution that is legally recognized. It is also a social institution about which many religions have many different things to say. The state has to have a definition of marriage and this definition should be a secular one.
Your proposal is an interesting one but it is not going to happen anytime soon and so it is not a realistic way of giving everyone equal treatment under the law. Your proposal also would not protect traditional marriage because, with the law out of the picture, SOME churches would start performing same-sex marriages.
Conservative christianity does not have the patent on “marriage”. Do you think Muslim states would be correct in prohibiting marriage between muslims and non-muslims? Government should be secular.
Your proposal could be achieved much more easily by simply saying to yourself that true marriage is in the eyes of God. The state can call marriage whatever it wants, but this is not “true marriage”. God and his institution of marriage are safe because no one can rewrite God’s laws. God (and Christians) are not harmed by the inaccurate use of terminology by others. State-sponsored marriage would just be seen by you as the civil union you are proposing, and true marriage in your eyes would be the one performed in a church in front of God. The state just uses the term “marriage” because it is shorter and correlates to a universal human institution that does however take many different forms.
Think of another social institution: education and graduation. You could take the view that one is only “educated” when one has learned something of the “truth”. There may be all kinds of people “graduating” from university who have not learned anything good and maybe even a lot of wrong ideas. Should we say that only certain kinds of learning should be included in the term “education”, and that those with a degree in Creation Science or in Climate Change (depending on what you think is wrong) should not be allowed to call themselves “educated”?
It’s just a word. A word for which you have a very important personal religious meaning, but a word that is used differently by different people. Misuse of a word can’t harm you or your God.