Since a lot of people have been commenting on Limbo in the past few, months I thought I would chime in with my two cents here.
Contrary to what many Trads have been saying, I do not think, in my opinion, that Limbo is a de fide doctrine. It seems to be an opinion of theologians. Now, let me clear up what I am saying: it is certainly de fide that those who die in a state of original sin with no other sin can nevertheless not see the Beatific Vision; original sin alone is enough to deprive one of the Beatific Vision. However, this doctrinal statement is not the equivalent of Limbo. Affirming the former does not necessarily imply the latter.
Nobody is doubting that those who die in the state of original sin are deprived of the Beatific Vision; to my knowledge, that has never been up for debate. Those who are saying that this is the teaching that the Holy Father changed are simply wrong. What is in question is this: does God intervene somehow on the behalf of infants who die in original sin in order to cleanse them and make them fit for heaven? This is the real question. So, while we can admit for certain that original sin would bar one from heaven, the question is whether or not God remits that sin somehow before they are judged. If He does, then there is no need to postulate the existence of Limbo, all the while maintaining the truth that original sin deprives one of the Beatific Vision.
I think there is Scriptural support for this position. In 2 Samuel 12, David is punished for his adultery with Bathsheba by the death of the child that he conceved by her. After he prays and fasts for the life of the child and it nevertheless dies, he gets up and cleans himself and calls off his fast. His servants ask him, "Why are you acting this way? While the child was alive, you fasted and wept, but now that the child is dead, you get up and eat!" In verses 22-23, David answers, "While the child was still alive, I fasted and wept. I thought, 'Who knows? The LORD may be gracious to me and let the child live.' But now that he is dead, why should I fast? Can I bring him back again? I will go to him, but he will not return to me."
Notice that David says, "I will go to him, but he will not return to me." Now, it is part of Catholic Tradition that the patriarchs and righteous kings, like David, went to heaven. David, after all, was a man after God's own heart; Scripture says that besides the Bathsheba affair, he did what was right all the days of his life. David is mentioned in Hebrews 11:32 as one of the heroes of faith who Christian Tradition has always placed among the blessed. Now, if we know with theological certainty that David went to heaven, and that David says of his dead infant that "I will go to him," then this seems to imply that the infant went to heaven, becaus he says that he will be with the infant, and we know that David went to heaven.
This is a good argument, and it seems consistent with God's mercy that He would desire to save those who have died in original sin through no fault of their own, but it has three weak points:
1) Just because God may have done that for David's son does not prove He does it universally; although I can see no reason why He wouldn't.
2) As far as I know, no Father of Doctor has cited this passage or made this case, though I may be wrong.
3) This is the same reasoning used by those who deny hell; i.e., we know that those who die in mortal sin go to hell, but perhaps God intervenes at the last moment so that nobody actually dies in mortal sin. However, this argument applied to infants dying in original sin is a lot more consonant with God's mercy and justice than the position used by those who deny hell.
That being the case, we must remember that Tradition is not a closed canon regarding everything. Tradition is living and is still developing; it has not fully developed, not will it ever fully develop until the end of time. There are some things still up for debate, and I think the existence of Limbo is one of them.
Let me restate what I said in the beginning: it is de fide that those who die with original sin cannot see the Beatific Vision. This does not imply that therefore all infants in such a state go to Limbo, for God could (if He chose) intervene on behalf of these innocent souls and remit their original sin at the moment of death, allowing them entrance into heaven. Based on the truth that God is just and would not punish people for what they are not responsible for, and that this seems to be the case with David's son, I believe that this is in fact what God does. I do not claim this to be truth, but only my theological opinion, for which I am open to discussion on.