Perhaps you can explain this to me then, since Rrhain refuses to answer. What is the reason that marriages and civil unions cannot be made synonymous under law? All it would take is a piece of legislation (perhaps inside the one creating CUs) saying that they are synonymous under law and legislation effecting one effects the other equally.
Up to now I thought I understood and agreed with your position Holmes. Suddenly it has gotten a bit more complex than I think is needed.
I thought you were saying:
Remove all references to marriage in the secular legal realm. Change all such usages to "civil union". Allow for same sex civil unions. Let the churchs perform, define and authorize "marriages" utterly separately from any reference to legal matters.
Then you have handled the traditional hang ups on the word, allow churchs complete freedom to do as they please with no reason to be afraid of being forced into anything they don't agree with.
You put everyone on the same legal grounds with no, I would think, constitutional issues.
Why risk there being any chance of the two things (marriage and union) being able to diverge in anyway. (There will be pressure to have that happen I'm sure.)