At the risk of coming late to this discussion and belaboring some point made pages earlier, I’ll throw in my two bucks - roughly the equivalent of the two cents when American had an economy.
The answer, my friend, is that Catholicism, Christianity in general and indeed Abrahamic faiths have NO interest in being shareholders in the public civil sphere like the rest of us. They consider themselves sole owners of the public sphere, and the rest of us live by their leave and at their sufferance. It’s not true of course, especially in this country which was designed to avoid that very thing, but 15 centuries of habit is hard to break…but we will. Law, culture and the tide of history, demographics, and time are all on our side. When it all shakes out, two or five or 15 years from now, gay people will get married in this country, churches STILL won’t have to, and a generation of us forum rats will have wasted untold billions of perfectly good ATP molecules banging away on keyboards…