Agreed. Mary is the Mother of God, because Jesus is God. She's the Mother of the human nature of His Divinity. His Divinity is Incarnate in Jesus, so if you deny she's the Mother of God, you are saying that God was not incarnate in the human nature of Jesus. You separate out Jesus Christ into 2 separate persons: one human, the other Divine. We must protect the term Mother of God in order to protect and guard the Incarnate nature of God the Son: God is born in Mary. God the Son! Not the Father, or the Spirit.