After doing a little research, I see that you are correct. And since you are correct, what I thought to be the best argument for Immaculate Conception is no argument at all. So I am back to the beginning seeing no use or argument for Immaculate Conception other than to elevate a supporting actress in to a lead role.
"So I am back to the beginning seeing no use or argument for Immaculate Conception other than to elevate a supporting actress in to a lead role."
The, "Honor thy father and thy mother," commandment seems like a pretty good argument to me, if you think God would follow his own commandment with respect to his mother.