Dear Fr. Hart:
The whole question needs to be discussed in terms of that phrase that was spoken by the Angel Gabriel: "Hail thou that art highly favored." What does "highly favored" mean as opposed to "favored" in the normal sense? As you probably know already, "highly favored" is the translation of the KJV for one word in the Greek, charitoō (χαριτόω) a form of charis (χάρις); and it is rendered "full of grace" in the "Hail Mary." As long as the Immaculate Conception is considered to be grace above and beyond the grace normally given (to speak in terribly inadequate terms), it may be reconciled to the rest of Christian doctrine. You mentioned sacraments, but remember that sacraments convey grace, and so for Mary to be full of grace (highly favored, highly graced) required no sacramental process, any more than the gifts of Confirmation (and, it seems, Consecration) required no sacramental process, because what happened on Pentecost, and later what happened at the house of Cornelius, made any sacramental process unnecessary. God acted to impart grace directly, even though that impartation normally requires sacramental acts of the Church.
In fact, on the blog I wrote a piece a few months back called "The grace of the sacraments."
Nonetheless, just because it may be reconciled to the rest of Christian doctrine, because it is all about grace (not that fairly useless concept called "merit"), does not mean it can be called a dogma. It has never been revealed, never been a subject addressed by Ecumenical Council, is considered incorrect by the Orthodox Church, was rejected by St. Thomas Aquinas, etc.
I agree with this and especially about her direct reception of grace. The problem for me is the idea that she would have been conceived without original sin. The problem is that our Lord would have in that case received unfallen human nature from our Lady. But then what is really accomplished by the hypostatic union? I think the older Eastern Orthodox understanding is that at the moment of the hypostatic union the humanity our Lord received from our Lady was completely healed of all the wounds of the fall and so the person of Jesus Christ was without sin. Also at the same moment of the hypostatic union our Lady was also healed of the wounds of the fall. I may be wrong but that's the sense I get from some of the Fathers. Gregory of Nazianzus: That which is not assumed cannot be saved. My point about the sacramental principle is that the hypostatic union is the prototype and the model of the how the sacraments work - that is the joining of ourselves to Christ.
Why was it necessary for the Lord to receive fallen human nature? St. Paul says only, "in the likeness of sinful flesh." What was the glory that was revealed on the Mount of Transfiguration? Divine Nature is invisible. The fall is inherited as a lack, not as a quality. Fallen nature lacks grace, and therefore is unholy.
Even after being beaten severely and crucified, the Lord could not die until he "gave up" his spirit.
I do not think it necessary for the Lord to have received the lack of grace that is, in essence, the fall. He received a full human nature into his Divine Person, whereas without grace, we have were born with less than full human nature, and certainly with nothing more.
But you are exactly right about the fall being a negation and not a quality. That's what he received from our Lady (our human nature not already saved human nature) and of course joining our nature to the Logos our salvation is made possible. The Orthodox reject the IM because they say that the West (I agree with the Orthodox) misunderstands original sin and they turn it into a positive quality - a "thing" instead of a negation. It seems to me that the IC pushes our redemption back to the conception of our Lady because that's when our healing first occurred. I think this is a problem caused by Vat. I and it is a shame because it is completely unnecessary.