Because we have allowed government to define “marriage” for its own purposes (such as taxation and regulation of estates), we have allowed government to define marriage as a social institution. That was fine as long as people in control of government were generally supportive of God’s original definition of marriage. However we have entered a time when a growing number of people in control of government want to redefine marriage for their own purposes, which in part is contrary to God’s definition.
Marriage is now far more a matter of politics and ideology than of private religious beliefs.
Therefore, for the sake of marriage as God defines it, it is time to remove from government the power to define who is married and who is not. Then gays could form whatever relationships they please but they could not force those who disagree to be enablers for those relationships. And we would not have schools that must teach that homosexual “marriages” are just as legitimate as heterosexual ones. Nor would we have owners of wedding photography services being threatened with arrest and being convicted of a crime for merely declining to artfully photograph a “marriage” they find morally repugnant.
Government, however, acts at the behest of the people it governs. Consider the Mormon Church which once endorsed polygamy even though it was illegal. In 1890, hey disavowed it. Today, the concept is more popular with reality programs like "Sister Wives". The taboo is gone and there are those who now argue that polygamy should be allowed.