Simple...is God not able to preserve Jesus from sin while in the womb?
If Mary has to be sinless then so does her mom and then her mom, etc.
The Immaculate Conception is not found in Scripture nor is it supported by the "unanimous consent" of the Early Church Fathers as admitted by the Catholic Encyclopedia online.
When compared to Scripture the Immaculate Conception is found to be in contradiction of Scripture.
I wasn’t thinking of Immaculate Conception. I’m not Roman Catholic. It does seem to me, however, that the answer you propose (and one I’ve considered myself) detracts from the idea of the hypostatic union - divinity and humanity in one person. In fact, so does the idea of the Immacculate Conception, in my opinion. Both require an exceptional intervention at the very beginning of Jesus’ life unlike any experienced by any other human being. Yet, the whole idea of the Incarnation is that He was born and lived as any other man. It’s just something that I’ve often puzzled over. The Eastern Church approaches this from an entirely different perspective.