OK so as a Catholic, while some other Christians also hold the same view, we are to beleive that Mary was sinless. This also ensures us that Jesus' birht could only be a virgin birth, according to Catholic doctrine (but by no means all Catholics) that sex before marriage is a sin. So, in oder for this to be true, this means Mary would have to have been exempt from or born without original sin. So, why would just one person be given this privilage? This obviously means that God can rid his people of original sin and even make us sinless beings. Why would He not do this for everone? Not doing it for everyone might seem like loving some more and others less.