I know what the belief is and it is foolishness.
God saved her from sin which she never committed?
If she had never sinned but rather had led a perfect life, then Jesus didn't need to die because she could have and she didn't need a savior.
And if God protected her from sin by having her born sinless, why doesn't or didn't He do that for ALL believers? If He could have done it for her, He could easily have done it for ANY human being.
Imagine what grief that would have spared the world.
Problem is, being human, He could not remove her sin nature from her. Then she wouldn't have been fully human. The only prophecy that needed to be fulfilled was that the mother of the messiah be a virgin. It says NOTHING about the need for her to be sinless.
That is going beyond what is written and demanding that it be believed, making it binding on the believer, is inexcusable.
SP stated it beautifully here on another thread.
As a matter of principle, I am unwilling to make binding, on either myself or others, any gray areas that are not clearly spelled out by the text of Scripture. It's way above my pay grade. Sure I'll try to think what's in those missing words. But I won't make up rules that God didn't make plain and lay them as burdens on others.
It's way above ANYONE's pay grade, no matter what they claim about themselves and being infallible.
NO ONE whoever they claim to be, has the right to make binding on anyone something that is not clearly spelled out in Scripture.