Marriage is a religious institution and has been defined as such as the covenant-bond between a man and a woman for thousands of years. The attempts by the left to redefine marriage isn’t - at its hearet - about equal rights, it’s about destroying the religious foundation of society’s most fundamental unit: the family.
Destroy the uniqueness and sanctity of marriage and you destroy the family. Destroy the family and government fills the social vacuum left behind. And this is nothing more than replacing traditional religion with the state.
Want to know why??? The left can’t control religion, they can only try to destroy it. But if the state supersedes religion, then the left can control that and everyone affected by it. The left is nothing if not persistent in its attempts to destroy traditional American society and replace it with their godless utopia.
Your critique of the attack on marriage and the left’s discomfort with religion is sound, though your starting point is flawed.
Marriage is not a religious institution, nor is it a state institution, but a natural institution. Our Lord appealed to the order of nature in His reply to the question about divorce, not to religion. Marriage existed before God’s call to Abraham, it existed before the Law, it exists in all human societies known to history, irrespective of their religious beliefs. And, it existed before the state, before kings or governments of any sort, in tribal societies (like, for instance, those described in Genesis).
The Church blesses marriage because Our Lord sanctified it with His first miracle and because it is within marriage that the calls to chastity and fecundity (be fruitful and multiply) can be lived out simultaneously. The state, when it is not arrogating to itself the purported power to define marriage, has, in almost all societies since the advent of governments, regulated marriage as a socially desirable institution (or as a competing source of social support).
In the Christian context, oddly enough, civil marriage preceded sacramental marriage historically. The earliest form of Christian marriage was a Roman civil marriage undertaken with the blessing of the local bishop, following which the couple would receive the Holy Eucharist at the same liturgy — there was not separate sacramental rite of marriage. Within the Empire, it was only when Emperor Leo VI promulgated a novella putting the Church in charge of marriage (and adoptions of children) in 912 that a specific marriage rite was composed. In the West, only slightly earlier, the Carolingian court was militating for the blessing of a priest to be considered necessary for a marriage — prior to that, evidently, local usages existed in which it was not.