Government is only necessary when natural laws are broken in any arena of life.
Regarding marriage, government exists to safeguard abandoned, abused or neglected children and/or abandoned spouses, heirs, and/or family members who are (or become) disabled.
Don’t fall into the marriage license trap. ALL American law comes from English common law and the English began issuing marriage licenses in the 14th century, this was done as a convenience to eliminate the banns of marriage that were issued earlier. To say that marriage isn’t any of the government’s business is the same as saying that ALL laws regarding marriage should be ignored and this would include polygamy, incest and the marriage of children.