My point is that you are presenting a very poor argument as a Catholic for the dogma of the Immaculate Conception. You will be caught in the trap of your own words if you argue “It was
necessary for Mary to be sinless in order for Christ to be sinless.”
Here’s the argument that’s inevitable if you present the dogma of the IC in the way you have–nonCatholic Christians (NCCs) will validly question your logic:
GT: “How do you explain God born into someone with Sin and not have Sin? God can’t have SIn, Mary can’t have sin.”
NCC: Then how could Mary be born of sinful parents? If Mary can’t have sin, then her parents can’t have sin.
See, Gary? You have no answer to the NCC when he presents that question.
RATHER! What is the best way to present the dogma of the IC is to say: Mary was sinless from the moment of her existence because it was FITTING that she who carried the Divine Presence be made of the “very best material” there is–pure, immaculate, and without stain.