The church should be able to perform SSM ceremonies, but the fact that their religion supports it doesn't mean the government should. If people don't want religion defining marriage then you have to have it both ways with it being left up to the people, not having a bias where religion is allowed to dictate government policy and recognition when it happens to be convenient for your views.
Tired of elections being between the lesser of two evils.When the debate is lost, slander becomes the tool of the loser. -Socrates
So if the rights, responsibilities, and benefits of Civil Marriage are not going to change and this "contract" issued (at greater expense) will be recognized the same as the government issues $35-$50 Civil Marriage Certificate...
.................... Then the reason for such a change makes no sense. We aren't changing what the impact of what Civil Marriage is, we are only changing who issues the piece of paper.