"Karl Keating, at least attempted a fuller discussion in his book, Catholicism and Fundamentalism. In speaking of the Greek term, kecaritomene, he alleged:
The newer translations leave out something the Greek conveys, something the older translation conveys, which is that this grace (and the core of the word kecharitomene is charis, after all) is at once permanent and of a singular kind. The Greek indicates a perfection of grace. A perfection must be perfect not only intensively, but extensively. The grace Mary enjoyed must not only have been as "full" or strong or complete as possible at any given time, but it must have extended over the whole of her life, from conception. That is, she must have been in a state of sanctifying grace from the first moment of her existence to have been called "full of grace" or to have been filled with divine favor in a singular way. This is just what the doctrine of the Immaculate Conception holds... (p. 269).
...However, if we look at Mr. Keating's presentation, it seems clear that he is basing his interpretation not primarily upon the lexical meaning of the word caritow, but upon the form it takes in Luke 1:28, that being the perfect passive participle, kecaritomene. Note that Keating alleges that the "Greek indicates a perfection of grace." He seems to be playing on the perfect tense of the participle. But, as anyone trained in Greek is aware, there is no way to jump from the perfect tense of a participle to the idea that the Greek "indicates a perfection of grace." First, participles primarily derive their tense aspect from the main verb of the sentence. In this case, however, we have a vocative participle, and no main verb in what is in actuality simply a greeting. (The fact that the Roman Catholic Church has to attempt to build such a complex theology on the form of a participle in a greeting should say a great deal in and of itself.) What are we to do with the perfect tense of the participle, then? We might take it as an intensive perfect, one that emphatically states that something *is* (see Dana and Mantey, A Manual Grammar of the Greek New Testament pg. 202), but most likely it is simply emphasizing the certainty of the favor given, just as the perfect passive participle in Matthew 25:34 ("Come, you who are blessed by my Father..."), 1 Thessalonians 1:4 ("For we know, brothers loved by God..."), and 2 Thessalonians 2:13 ("But we ought always to thank God for you, brothers loved by the Lord...") emphasizes the completedness of the action as well. No one would argue that in Matthew 25:34, Jesus means to tell us that the righteous have a "perfection of blessedness that indicates that they had this perfection throughout their life, for a perfection must be perfect not only intensively, but extensively" (to borrow from Mr. Keating's presentation). The application of Keating's thoughts to any of the above passages results in foolishness. Hence, it is obvious that when Keating says that the Greek indicates that Mary "must have been in a state of sanctifying grace from the first moment of her existence to have been called `full of grace' or to have been filled with divine favor in a singular way," he is, in point of fact, not deriving this from the Greek at all, but from his own theology, which he then reads back into the text. There is simply nothing in the Greek to support the pretentious interpretation put forward by Keating and Madrid. Therefore, Madrid's statement, "This is a recognition of her sinless state," falls for lack of support. The angel addressed Mary as "highly favored," for, as he himself said, "Do not be afraid, Mary, you have found favor with God."
This should make perfect sense for anyone that understands that God would not join flesh with a sinful creature to become incarnate. Joining flesh with a sinful Mary would mean that Christ takes on a sinful nature because He took a flesh from a sinful human nature to become true man and true God. Don't confuse this with Christ dying for our sins because he did not have a sinful human nature to do this. His nature would be sinful if Mary's was sinful since he joined flesh with her
This is plain common sense.
If Mary sinned than God attached Himself to sin and is flawed in His human nature. It's really that simple!