Ah, whose opinion is this?
How can you live in a society that is based on the Law as received from God by Moses and not discern both good and evil? For Mary to be sinless, she must have obeyed both the moral and ceremonial aspects. Did she not say, "How shall this be, seeing I know not a man?"
Doesn't this imply that she knows it would not be good to "know" a man--even her espoused husband--during the espousal time?
I would think this theory would run into a lot of opposition.
The Catholic Church did...
To me, it's really, really simple:
If you are "preserved exempt from all stain of original sin." which is the fall of man in the Garden, you are now free from the "knowledge of good and evil"...
Either Mary is sinless or a sinner...
It can't be both...