Could you explain the following to me?
You believe that Mary had to be sinless because she was to have a sinless Son of God
Did Anne need to be sinless to have a sinless daughter that would be sinless? Then did Mary's grandmother need to be sinless so her sinless daughter could have a sinless daugther that would have a sinless Son of God?
If God in a moment of Grace could cause Mary, who had a sinful mother AND a HUMAN sinful Father to be born sinless was he UNABLE to have His sinless Son born to a woman that bore the original sin of man?
You're 100% right RnMom--that is a problem and it's why the Church didn't say it was logically imperative that Mary had to be sinless for Christ to be sinless. It said instead "it is fitting" that Mary be sinless. It was not a logical necessity, but it was wholly appropriate that God grant it. As the ark that held the stone tables of the Old Law was pure and inviolable, so all the more would the ark that carried within her the Word would be pure and inviolable as well.
So when the question comes of how Jesus was able to be fully human without succumbing to the curse of Original Sin, there are two options here presented: that Christ was essentially placed in Mary's womb as a fully fertilized egg to which Mary contributed no genetic material, or God chose to bend His own rules and "suspend" the curse He placed upon the human race (or rather that the race brought upon itself).
Greek and Roman mythology tell of Gods coming down and having sex with humans, and essentially that's what the doctrine of the Immaculate Conception puts forth. I have every respect for Mary as a saint and a good example of submission to the will of God. It's the Roman Marian doctrines to which I am hostile.
Regarding the Immaculate Conception, Jesus took 100% of his humanity from his mother. It would seem only fitting that Mary would be sinless to pass on her genetic code to her son.
In addition, I believe we are in agreement that Mary is the second Eve (as forementioned in Genesis) and Eve was created sinless. It is logical that Mary was also created sinless.
To me, Immaculate Conception is not a difficult concept considering that God chose Mary to carry His humanity, Jesus Christ, who was fully God AND fully Man. And Mary, of her free will, said YES to God (which, He of course knew she was going to do).
God bless!