"What about the vision of Fatima!?!?" is a common wail.
Well, let's think about Fatima for a moment.
On July 13, 1919, the Blessed Virgin Mary herself taught the three visionaries this prayer:
O my Jesus,Now, think about that.
forgive us our sins,
save us from the fire of hell,
*lead all souls to heaven,*
especially those who are in most need of Thy mercy.
Is prayer ever useless? Obviously not.
Would Mary ever insist we pray for something that is useless? Again, obviously not.
God doesn't have us do useless things.
So, if human souls were in hell, why would Mary ask us to pray in 1917 that all souls be led to heaven? There is no way to get out of hell - that's de fide. Yet we are asked to pray that all souls be led to heaven.
Now, prayer is a timeless act. It's effects can ripple backward in time as well as forward in time. Therefore, it must be possible for us to have theological hope, rooted in God's own divine mercy, that all human persons be saved. Hell would still exist, and would still be occupied by the fallen angels. It would not be empty. There would simply be no human persons in it.
If we didn't have the theological right to hope for this - indeed, the duty to hope for this - then Mary would never have taught us this prayer and asked us to pray it. And this hope cannot just be a natural hope, for no one can have a natural hope for heaven. If our entire basis to hope for heaven lay only in our human nature, then we are all doomed to hell. The only way we can attain heaven is through God's own gift of supernatural grace. That is why our hope for heaven, whether it be for ourselves or someone else, must always be a supernatural hope, for only God's supernatural grace can accomplish this end. To say we can only pray this prayer with a natural hope is to say that Catholics are allowed to be Pelagians, which is absurd.
So, Fatima has a certain tension within it. On one hand, we have the visionaries seeing people falling towards hell, on the other, we have Mary teaching them to pray that all souls end up in heaven.
Conclusion The only conclusion we can reach is this: the souls the visionaries saw moving towards hell, even at the moment of their death. even those who died in the past, can be saved for heaven at the moment of their death by our (future) prayers and sacrifices before God's throne. The timeless nature of prayer is also about the only thing that would explain why none of the nasty events Mary described at Fatima actually happened: Russia would eventually be properly consecrated at some future point, so none of the described disasters actually took place.
If anyone wishes to stand on Fatima in order to demonstrate that not all human beings are saved, s/he stands on a very weak reed indeed, for in the very same visionary event, the Blessed Virgin Mary commands us to pray a prayer that assumes all human beings can, in fact, be saved. Since Mary did teach this prayer and command we pray it, we can correctly conclude no human being is yet in hell, and we can also conclude that it is our duty to hope every human being attains heaven.
The papal preacher apparently agrees with this view.