The theory behind gay marriage, in short, was the theory behind the entire secular left: society and the state are the all-powerful forces on which the life of the individual depends, and the most important political task—indeed, the most important task in life—is getting this irresistible power on your side. Once you gain social and political power, you hold on to it by making your preferred views mandatory, a catechism everyone must affirm, while suppressing all heretical views. In this case, to gain social acceptance of homosexuality, you make the affirmation of gay marriages mandatory while officially suppressing any dissenting religious views.
Hence, the Secular Inquisition, which we should have expected all along.
Except that it turns out to have the opposite effect in the long run, as the history of the original inquisition reveals. A big part of the reason for the centuries-long decline in the influence of religion in the West is the aftermath of its attempts to protect its social monopoly through coercion. I don’t think the Church has ever really recovered from the legacy of the Spanish Inquisition, which served to discredit religion by associating it with brutality—an image that has lived in infamy for centuries, down to its use in a certain well-known Monty Python sketch.