Because we all have this "stain," a "merciful God"(?) damns the unbaptized to spend eternity suffering in hell even infants who die. Or so the story goes.
Later on it was agreed that this was rather harsh, so the unbaptized not guilty of any serious sin were consigned to 'Limbo" a state of "natural happiness" in which, however, the person is denied the beatific vision of God which was important for some reason.
Many Catholics and Protestants haven't kept up so don't realize that Pope Francis abolished it obviously because it was realized that it was a fiction.
However, the full effect of this hasn't been felt yet. The Catholic Church's "doctrine" of Mary's Immaculate Conception is also void if there is no Original Sin to begin with.
