Along with the dangerous "Co-Redemptix" title, other titles given to Mary include some I never use. I refrain from the title "Our Lady." My reason is very simple. When we call Jesus the Lord, as we call also the Father and the Holy Spirit, it is a very special use of the word "Lord." Because the Jewish people ceased to pronounce the Name of God (יְהֹוָה corresponding to our Latin letters YHVH) after returning from captivity in Babylon, it became the normal rule to substitute the word Adonai (אָדוֹןי) when reading aloud from the Torah. The word Adonai means "Lord." Therefore, the use of the Greek word kyrios (κύριος), the standard translation, when used for a Person of the Godhead, that is "the Lord," means more than merely a human master or nobleman. In that context it means God. Therefore, to speak of Mary as "our Lady" makes me uncomfortable, to say the least. God has no consort, and Mary is not the Lady, that is not an equal sharing the Divine nature among the three Persons we call the Lord. I would not accuse anyone of meaning it that way; but, I refrain from so using it. Others may, and I will not judge them unorthodox.
Likewise, I see no reason to use the title "Queen of Heaven." I know about the twelfth chapter of Revelation, and how Mary is mysteriously portrayed there as the chief representative of the people of Israel (as signified by the elements from Joseph's dream about Jacob, that is Israel, and his heirs; the sun, the moon and the eleven stars-Gen. 37:9,10), giving birth to the Messiah. But, that hardly justifies insulting the Blessed Virgin Mary with a title that brings to mind the Ashtoreth (Jeremiah 7:18 & 44:17-25). She deserves better than to be called by such a title, especially concerning Heaven where everyone present sees the throne of God, and concerning which we have no revelation about a queen, and no need. The title "Queen" suggests the need to perpetuate a dynasty. I would not accuse anyone of meaning it that way; but, again, I refrain. Others may use it in good faith, and I will not judge them unorthodox.
But, concerning the title "Mother of God" I say only "amen," without any caveat or red flag whatsoever.
It has been argued that "God-bearer" is a more exact translation of the word Theotokos. I have no argument with that, as an exact translation (though I still insist that "Birth-giver of God" comes across as a heroic, if not silly, measure to avoid the word "mother"). But, the nature of language is such that sometimes an exact translation loses something in...translation. Even if someone may argue that the exact translation suffers no loss, history has assigned the expression "Mother of God" to our common western vocabulary (not only in English, e.g., the Spanish Madre de Dios). I understand the argument that the ancient Church could have used an unmistakable expression, incapable of any other translation, and chose not to do so.
Perhaps, because they were writing in a time of emergence from Pagan culture, the ancient writers in the Church really did mean to keep their distance from any suggestion that the Godhead has an origin in some sort of mother. But, even so, it is unrealistic to suppose that, in modern times, anyone anywhere might think that Christians believe in an emergent Deity coming from an origin that gave birth to the Divine Nature. Even if the expression "Mother of God" could have been misunderstood in the Hellenistic culture of the fourth century, today the shocking boldness of the expression, loaded with its built-in paradoxical punch, creates the demand for an immediate resolution of the logical tension it creates. The only resolution that the informed mind can provide is in Scripture: "The Word was made flesh, and dwelt among us..." (John 1:14). The expression, "Mother of God" leads directly to the doctrine of the Incarnation, without any possible alternative destination.
The expression states clearly that Jesus Christ is fully Divine and fully human. Therefore, the term fights against Arianism on one hand, and at least one form of Gnosticism on the other. That is, by affirming that Mary's Son, the Man Christ Jesus, is rightly called God, it refutes Arianism. By affirming that this same Person rightly called God is Mary's Son, the Man Christ Jesus, it refutes the Gnosticism of Marcion, the Jesus who merely appeared to be human, but who left no footprints behind him because he was not really human. Against these heresies we use the expression, "Mother of God" for the Blessed Virgin Mary. In saying that, we say that Jesus Christ is fully God and fully man.
"Western" Trinitarianism, apologia
We were told, in comments, that the word "God" properly speaks of the Father only (an unanticipated objection, since it is "God" that puts the Theo in Theotokos). This view is commonly expressed, normally by converts to Orthodoxy or even by lifelong Orthodox Christians, but only by those who want to place far too much emphasis on supposed differences between Orthodoxy and "Western" Christianity. In trying to be as different from "Western" Christians as they can, some of their writers go too far. For example, Fr. Thomas Hopko has made too much of the distinction between Ho Theos and Theos (τὸν θεόν and θεόν) in John 1:1. That is, between how the grammar added the word ho (τὸν), which means only "the" when speaking of the Father. But, the simple fact is, the word Theos itself is what truly matters. The Second half of John 1:1, translated into English very literally, would be "And the Word (λόγος) was with the God (τὸν θεόν), and the Word (λόγος) was God (θεόν)." But, the same word, Theos, is unmistakable.
At this point, it is reasonable to ask about verse two. Why would John repeat a point already made? "The same was in the beginning with the God (οὗτος ἦν ἐν ἀρχῇ πρὸς τὸν θεόν. )." The answer is, John was not repeating the same point, for sheer redundancy would have been unnecessary. Clearly, this third invocation of Theos refers to the Holy Spirit. Like the Word (who is also called the Son), the Holy Spirit derives His existence from the Father. In language that points to truth beyond our comprehension, the Gospel of John teaches that the Word is the only begotten Son, that he is eternally begotten of the Father; and it teaches that the Holy Spirit eternally proceeds from the Father. Neither the Son nor the Spirit were or are created; both are equal to the Father, and yet both come from the Father, One we say begotten the Other proceeding. Both are eternal, without beginning or end; both are equal to the Father, each Person having the same uncreated Nature (physis, φύσις) as God.
To get to the point, about John 1:1,2, if the Father is somehow the only Person properly called "God" because He is "the God" or Ho Theos, why is the Holy Spirit, in verse 2, who derives His eternal existence from the Father no less than does the Son, also called Ho Theos? The simple answer is this: Ho, or "the," is a separate word that does not change the meaning of Theos. The issue is grammar, not meaning. To suggest otherwise leads us to the dangerous business of making a distinction between degrees of Divinity -- not Degrees in Divinity as an academic subject, but degrees to which a Person (or hypostasis - ὑπόστασις) is more or less God, or perhaps merely a lesser "god" in some sort of pantheon. In attacking the "Western" concept of the Trinity, with its somewhat more pronounced emphasis on the equality of each Person of the Trinity, some of our Orthodox brethren lay the unstable foundation for arguing the Arian heresy. They will not make that argument themselves (thank God for such mercies), nonetheless they cannot help but provide the rationale for those who do.
To suggest that the Son is God, but not quite as much God as the Father, would be heresy. These "Eastern" Orthodox Christians do not go there themselves, or so I hope, but they make straight the way to that heresy. I wonder why not being "Western" is worth the risk to them. To hear some of them use phrases like "the idolatry of the Son," ought to send chills up our spines. I would urge them to stop worrying about the alleged dangers of "Western" Christianity, and make a better effort to steer clear of the Arian heresy. They need to do so even if they risk sounding like the allegedly inferior "Western" Christians, those they seem ashamed to call brethren.
When we say "God" we speak in light of the full revelation of the Divine Name, into which we were baptized, that is, "the Name of the Father, and of the Son, and of the Holy Ghost." (Matthew 28:19) Obviously, when we use the word "God," the context gives us all the clarity we need. When we speak of the Son of God, we emphasize the distinction between the Father and the Son. When we say "the Spirit of God," we make the distinction between the Father and the Holy Spirit. In fact, when Saint Paul and Saint Peter wrote the words, "the Spirit of Christ" (Romans 8:9, Philippians 1;19, I Peter 1:11), they made a distinction between the Holy Spirit and the Son.
Likewise, when we call the Blessed Virgin Mary by the title "Mother of God," it should be obvious to everyone that we speak of God the Son, or Word. "And the Word was God...and the Word was made flesh." Without context, the word "God" all by itself, speaks to us of the Father and the Son and the Holy Ghost. That is how Saint John used it, and therefore what he taught us, in the opening of his Gospel.