In this thread one of the answers states that Catholic tradition has Mary as sinless from conception (if I read it correctly). I don't want to sound flippant here but this begs the question: if God could do it for Mary with no problem, why not do it for everybody? I mean, why even bother with the crucifixion at all? If you think about it, He could have done the same thing with all of Adam's first generation and poof! Problem solved. Why go through all the trouble?
If God could make Mary sinless, why not anybody else?
God being omnipotent, could have created the world differently and made it that we were all "immaculate conceptions", but he chose not too. We must respect his decisions.
First of all there are only two people the Catholic Church recognizes as being preserve from original sin: Jesus and Mary. However there are two other people who were created prior to the fall and were thus at one time in a state of grace (sinless) and in union with God: Adam and Eve.
Your question now begs another. If mankind were to have been preserved from original sin, would that mean that we would have been completely sinless until we died?
Part of Mary's graces in receiving the gift of the Immaculate Conception is that she cooperated with the supernatural graces given her in order to avoid sin also. Mary too, just like us was tempted to sin. Unlike us, she conquered the temptation she experienced in this world and remained sinless.
One can not stress enough the fact that the Virgin Mary like us had to diligently work out her own salvation, even though she received special graces because she was the mother of Jesus, who is called the Christ.
Although preserved from Original Sin, Mary still was a human being like the rest of us. But, she was given preventative redemption, meaning that the grace she was given at her conception was in anticipation of Christ's sacrifice on the Cross.
What is true is that her very personal sinlessness gave her a deep sense of what sin and evil are. It only caused her moments of suffering to be intense to a point we cannot fully grasp.
If you want to ask what sin is, don’t ask an evil person. The one who knows sin is the one who is in a deep and loving relationship with God, and one who suffers from the evil of others.
The idea that Mary was never tempted is trumped by the simple fact that Satan tempted Jesus himself. For Satan, Mary would have been a real prize. So understanding Mary’s own humanity, as perfect as it is, consider what would be one of the most painful experiences she or anyone could have? - The Loneliness of Mary of Nazareth.
So in the end, God could have created us all sinless at birth , But would we have all preserved our sinlessness? Who knows what form of temptations Satan would have mustarded up against us then?
But for myself, the Exsultet say it all:
O certe necessárium Adæ peccátum, quod Christi morte delétum est!
O felix culpa, quæ talem ac tantum méruit habére Redemptórem!
O truly necessary sin of Adam, destroyed completely by the Death of Christ!
O happy fault that earned for us so great, so glorious a Redeemer!
Mary's immaculate conception, like our redemption, resulted from the merits of Jesus Christ, in particular His crucifixion. So that's why God had to "bother about the crucifixion".
In more detail, from the bull "Ineffabilis Deus" of Pope Pius IX defining the dogma of the immaculate conception:
"We declare, pronounce, and define that the doctrine which holds that the most Blessed Virgin Mary, in the first instance of her conception, by a singular grace and privilege granted by Almighty God, in view of the merits of Jesus Christ, the Savior of the human race, was preserved free from all stain of original sin, is a doctrine revealed by God and therefore to be believed firmly and constantly by all the faithful."
Note in particular the phrase "in view of the merits of Jesus Christ, the Savior of the human race"; without Christ, Mary would have been in the same sad state as all the rest of humanity.
As an ordinary part of the human race, born into the world the ordinary way, Mary was not without sin. Romans 3:23 teaches that all have sinned and fall short of God’s glory, and there is nothing in the Bible to suggest that Mary was an exception to this rule. The apostle John wrote, “If we claim to be without sin, we deceive ourselves and the truth is not in us. If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness. If we claim we have not sinned, we make him out to be a liar and his word is not in us” (1 John 1:8–10). The “we” in this passage includes Mary, the mother of Jesus. To claim Mary is without sin is an example of “deceit.”