Sorry, you have the independent and the dependent variables confused. People will enter into any type of relationship that pleases them. In some societies one or more of the parties may be in the relationship against their will. Some relationships produce children. Only some of these relationships qualify as “marriage” as God defines it.
Some, but not all of these relationships are the building blocks of society. We see communities where a woman has 6 children by 5 different men, that the children grow up more often in poverty, dependence and even prison. I would reject that such relationships are any sort of foundation to a society that we would want.
Beginning with interest in eugenics by progressives, states have attempted to regulate private relationships and to impose restrictions on who can marry.
Having said that, notice that no state attempts to restrict the conception of children. At the very moment that young people must apply for a license to marry, their friends are cohabiting and conceiving children without fear of being arrested. Few “hippie communes” with feral children were ever raided by police.
No law is going to stop random copulation by drunk youth, and the resulting conceptions. People who insist that government has a role in marriage are fooling themselves and being enablers for State power that it never should have had.
So, some people are screwing up the principle upon which our entire civilization and form of government is premised and organized, and your solution is to dispense with the principle.