...are you suggesting that only couples that are involved in a particular religion gets to hold the tittle of "married"? What about those who do not attend any type of religious organization?
If a government(s) went to the huge hassle of rewriting all laws to avoid using the word "marriage" it wouldn't help the anti-gays a tiny little bit.
Anyone can form any kind of organization and grant a marriage to anyone. It would have no meaning in law and therefore no control in law.
In fact, this approach would open the word "marriage" to anything that anyone wanted to call a marriage (to your dog?) while civil unions would be the word that keeps some meaning.
Anyone who suggests that just having civil unions for all is a solution to the conflict hasn't thought it through. It would be a fair and good thing to do but would be much, much more expensive and complicated than just opening up a legally defined marriage to those who should get it and it would have exactly the effect that the anti-gay crowd are afraid of: it would degrade the meaning of the word marriage by leaving it with no meaning at all.