Whether you know it or not, you've stumbled upon the reason why Pope Blessed Pius IX thought it was opportune to infallibly declare the Immaculate Conception of the Blessed Virgin Mary as "a doctrine revealed by God and therefore to be believed firmly and constantly by all the faithful" (Ineffabilis Deus).
The implications of the Virgin birth are staggering. But Protestants reject them. They want to put aside the christological questions and treat Mary as pretty much the same as Elizabeth.