“It is impossible for Mary to have been sinless, she’s human and had a normal birth.”
This is where the Immaculate conception comes in. Christ protected Mary from sin.
“Sin is passed by the seed of man is what I was taught.”
Which is why Mary’s immaculate conception is the break in the chain. Remember Christ is fully Man. IF sin is inherited AND Christ is fully man, then he inherits a sinful nature.
If sin is inherited from the father, the Holy Spirits conception of a child in Mary would not have passed on sin as God has no sin.
So I understand Christs sinlessness. But If God could keep Mary from sin, while being born to a human set of parents, there would be no need for Christ in the first place.
So while Christ’s sinlessness I can see the need and fufillment of Gods plan in, the sinless Mary thing is not only not needed, but invalidates Christ.
I think at this point the Mary thing is more a throwback to the incorporation of Ishtar and the child than anything logical or spiritual. It is more mother worship than God worship. While in Rome for a few months I toured many Catholic churchs and noted that there were two basic types, the ones with lots of saint statues and huge pictures of Mary with a little Child, and the ones without all the saint worship, small pictures of Mary and huge pictures of Jesus with the centerpiece a crucifix.
So I suspect even within the Catholic family there is a divide on this issue. Quite interesting really.