I'm operating under the assumption that the "civil union" would be a separate legal construct, distinct from marriage, that defined its own rights for managing property, etc. Sure, it would be trivial to just say "gays can go down to the court house and get a civil union, and all civil unions should be treated exactly like marriages for the purpose of the law." But then civil unions are exactly the same thing as marriages.

> " But then civil unions are exactly the same thing as marriages.

That's right. Proponents of civil union say that everyone (including heterosexuals) should be granted civil union, and somewhere in the anals of law it should say "civil union is legally equivalent to marriage".