Universalism and Our Lady of Fatima

The following argument (which is inspired by a comment that Peter Kreeft made in this interview with Matt Fradd) strikes me as sound:

1. The Blessed Virgin would not instruct anyone to pray for something impossible.
2. The Blessed Virgin instructed the children of Fatima to pray that Christ will "lead all souls to heaven."
3. Therefore, it is possible that Christ will lead all souls to heaven.

One could take this on its own as an argument for the possibility of universalism, against those who believe that Catholics are committed to at least some persons being damned. This would be significant enough on its own; however, I believe we can go further. Consider:

1. If it is possible for all to be saved, then all shall in fact be saved.
2. It is possible that all be saved.
3. Therefore, all shall in fact be saved.

The idea here is that defenses of infernalism typically depend on the assumption that God cannot save everyone (e.g. because the damned freely choose to reject him, and one must freely choose salvation). But if it is possible for Christ to lead all souls to heaven, then things become much harder for the infernalist. They would now have to argue that Christ could save all, but (for one reason or another) he simply won't. And this is clearly preposterous.