In his debate with James White on the Marian Doctrines Roman Catholic Apologist Gerry Matatics makes the following argument for the sinlessness of Mary:
P1: Honoring your Mother entails that if S has the ability to keep S's mother sinless then S would bring it about that S's mother is sinless
P2: Jesus has the ability to keep his mother sinless
C: Jesus brought it about that his mother is sinless
The problem with this argument is obvious: When Mary was born and inherited original sin at that time she was not Jesus' mother (Jesus with respect to his human nature was not born). So Jesus at that time was not under obligation to bring about her sinlessness. Another obvious problem with this argument is that the commandment says to honor your *father* and your mother. This means that if this argument was carried out consistently then we ought to think that Joseph was sinless, but neither Catholics nor Protestants teach this. All this to say: arguments like these are entirely desperate attempts to hide the obvious truth that Roman Catholic churches teachings cannot be justified by scripture and right reason.