Lets be clear, when politicians like Marco Rubio talk about a danger to the survival of Christianity, they're not talking about survival or about Christianity, they're talking about a danger to the power and authority of a certain definition of Christianity that many Christians would call by a different name. Whether or not he seriously thinks Christianity will die out, that nobody will or could be a Christian if the US allows people of the same sex to be party to a civil marriage contract, Rubio, as most politicians do, is using words in a consciously deceptive way.
How do we define, or more importantly how does the government define Christianity? In fact the constitution forbids it to do so . There are and have been many such claimants to the robe and sandals and the reins of government, so Marco is surely being less than honest to refer to Christianity when he means his Church and its rules. He's being a damned liar by offering us fables about the origins of our laws or arguing from tradition.
Some people simply don't define Christianity as a secular authority primarily established to restrict the private sexual thought and behavior of all people. Certainly not since they never legitimately had such power, nor does the American Constitution state or imply that any legitimate power be given such authority, nor is or government empowered or obliged to "save" any religion, tradition or religious practice.
There is no unified, undisputed definition of Christianity or of any religion or the doctrines thereof and to say anything else is prevarication. If the legalization of an inherent right of Man is a blow to Christianity I would suggest that a weakening of Christian authority must have preceded it as is the case in Ireland where years of censorship, control of education, marriage rights, reproductive rights and lastly the widespread abuse of women and children, turned Christian power into a thing of public loathing and anger. Indeed Democracy and the right to elect a government only succeeded after the Church lost the power to prevent it.
Rubio, like many of his Evangelical allies are consciously taking the risky position of posing what people approve or see as a right to be protected, as being the enemy of their tribal authority. He needs to remember how all the other shibboleths have fallen, interracial marriage, blue laws, censorship, the inferiority of women and indeed slavery -- and fallen despite claims that Christianity was in jeopardy and God would punish us all for allowing it. Sooner or later the prophet has to deliver or be swept away. It's not a good thing to be in power when the argument from tradition, the argument from authority is stretched so far that it snaps.
No, Christianity in some form or another will survive. Perhaps a kinder, gentler more respectful form. It's Marco Rubio and the various crusaders against the right of the people to decide their own rights who are at risk. I truly doubt that Rubio isn't aware of the truth of that, or that he is unaware of the kind of State toward which the manifest destiny of free people inexorably trends. It's a shortsighted lust for power and with all his dishonest nonsense about Christian tradition, that tradition has never been about freedom of conscience or any kind of liberty.
As with his mumblings about how our Cuba policies have not failed after 50 years, it's a defense of blind, intransigent, self justifying power and authority and an attack on objectivity and the liberty of the citizen. Make no mistake, Rubio is against the idea that the government is of the people, by the people and for the people and legitimized only by the people and not by gods or politicians who pretend to speak for them.
One gets the idea that Pope Benedict is well aware of all this and is concerned that Rubio's way of thinking is making the Church not only irrelevant, but unsustainable in the modern world, but as the Chinese were wont to say from ancient times, "Heaven is high and the Emperor is far away.". The Vatican has one policy, the parish priest and the pandering politician have another. Down at the level where the rhetoric hits the road it's still the old beast.
Christianity has survived a great deal as it always has -- and it will change a great deal as it always has. If anything is in danger, it's the guy staking everything on holding back the tide.