It doesn't diminish Christ at all! This is how man thinks. Through God, "all things are possible." Remember, Jesus is true God, and true man. Mary is a creature, but she was spared the stain of sin, through the mercy of the Holy Trinity, of which the Son desired to come to earth to save us.
by who's supposition ? - I still dont see a Scriptural basis for this....and am starting to conclude one does not exist