You know it's kind of like Amway or Earthlink or one of them. For every person I get to worship Mary I get one free month of grace.
Actually, what is it is that the "is" in "Jesus is God" is not commutative. If I say "Jesus is God, that is not equivalent to "God is Jesus", even though God doesn't come in pieces or parts.
But the very nature of your disagreement is consistent with our assertion that to say "Mother of God" about Mary is a Christological and Trinitarian issue.
God isn't Jesus????? Wow! Did you tell the Pope that????? I'm sure he'd be interested in hearing it. In fact, he might stop worshipping Mary for 5 minutes just to hear your explanation before he excommunicates you as a heretic (oh, you don't do that so much any more do you ;))
Hey, saying Mary preexisted God should be equally as valid as Mary Mother of God. So, there you have it MARY PREEXISTED GOD and to say anything else is equivalent to Polytheistic Nestoriarianistic heresy! I declare it so by the authority of the council of Ephesus.