Jesus didn't need a sinless vessel to be born sinless, any more than the Ten Commandments needed perfect contour and ornamentation of the ark to be efficacious. But a certain dignity was required of God. They may have been wandering around impoverished in the desert, but the vessel in which God would be carted around was meticulously planned, by His own decree, with immense dignity for His presence. Nazareth was likewise an impoverished, scorned community, but that did not lessen the dignity required of the vessel which would carry God's physical and spiritual presence for nine months. Anything short of perfect would place the dignity of Jesus Christ below the dignity of the Old Law, which Jesus came to fulfill. Insisting that Jesus could be born to any old "broad" in any spiritual condition doesn't jive at all with the rest of the Bible and relegates the Lord to a place lesser than Aaron's staff.