Out of curiosity… why is this particular dogma hard for you to accept or believe? It seems to me this one would be fairly self evident.
The bible says that God gave specific instructions to Moses to build the Ark of the Covenant, using incorruptible and pure materials (specific woods that do not decay, gold a simple of eternal lasting.) He had it made with precise measurements, and to exacting specifications. This was a container for the written Word…
The Bible says that God knits every man in the womb, that He knows each of us completely from the very moment of conception. We all believe that God creates each of us specifically as us, and that each person is designed specifically the way they are. As they told us in elementary school (well some of us) God doesn’t make mistakes.
Now knowing that, do you find it hard to believe that God would make the container (Mary) for the very Living Word (Jesus) without putting time or effort into it? That God knits you and I in the womb and creates us specifically for our purpose… but not Mary… she was just a random accident? That God as an after thought said “Oh yeah… I need someone to raise me… ah anyone will do… roll the dice.” No… God would not have sent his very Son, the Logos… into this world into just any person… but into the womb of the very person he created to exacting measurements, to be incorruptible.
Just like the Ark, which was not allowed to be touched by man… so too was the Living Ark, Mary, not entered physically by any man, including Joseph. Just as the Ark was made of pure materials, incorruptible… so too was Mary made with purity in tact, and made with the heart and soul of a woman who would live to God’s will always, assenting with a Yes for all time… forever sinless.
For me, this one was easier to accept than many other Catholic doctrines.