Marriage should be none of their business.
It would really screw up their marriage-destruction plans if religious people just got married in the Church and dispensed with registering with the government.
Not all people are religious, Islam is a religion and they are polygamous, Mormonism is a religion, Homosexual religions are religions, anything and everything can be a religion.
I don’t want Sharia law to tell me what marriage is and to dictate divorce law and custody rights, and division of property and assets, or decide who is considered married for the military and federal employees, etc.