But Fatima was not merely a private revelation. That's the error
How could a public miracle, predicted in advance by 6 months, and given from God (approved by the Church as such) for the purpose of helping the faith of believers (and faith is the most precious thing we have in this life) be a "private" matter?
Certainly the message as given to the shepherd children was private, inasmuch as it was "secret," but that was not to remain the case. The secrecy was for a temporary purpose, such that the Miracle of the Sun would be effective for what it was intended by God Himself. And don't forget, the Miracle of the Sun, as great as it was, and beyond imagination -- far and away the most astounding public miracle in the history of the world -- would have been even GREATER (but we cannot imagine how so) if the three children had not been kidnapped on August 13th, 1917.
No, it was much more than private
, because it was given to those who came at the time, all of whom are most likely deceased now. They came from far and wide, most of them from Portugal, and they numbered between 70,000 and 100,000 people. This was not a "private" event, any way you try to slice it. And the story lives on, and the miracles continue, therefore it is given to all men worldwide for all time to come, and that means it is not "private." Why is this so difficult to understand?
There is a third classification of revelation, in between Apostolic revelation (which was given during the lifetime of the Apostles and applies to everyone) and private revelation (which is given to an individual and is only applicable for the personal spiritual life of that person). The third type is public prophetic revelation, and it is described in Sacred Scripture itself.
The Miracle of the Sun was a public event, predicted in advance by the prophesy of Our Lady, and confirmed the revelation given to the shepherd children as a "secret" to be divulged at a later time. Therefore, the Message of Fatima belongs to this third category, public prophetic revelation.
As such, it is not strictly binding as Apostolic revelation is binding on all the faithful, however, it is not only applicable to the seers themselves, as if it were private revelation. That is, we are not absolutely required to believe it with full assent of mind and will, however, we would be remiss to entirely dismiss it as so many pitiable unfortunates are wont to do. However, when the time comes, and it would become defined as a dogma of the faith, at that time we would cease to be Catholic by denying it, just as we would by denying the Immaculate Conception or the Assumption of the Blessed Virgin Mary body and soul into heaven. There was a time, not that long ago, when we could debate those things, but no more. They have been defined as dogmas of the Faith for all human creatures to believe if they are to be saved. I'm not saying that it ever will be defined, but merely giving that as a point of reference.
The coronation of the Blessed Virgin Mary Queen of Angels and of men has not been defined either. But it is the last decade of the Rosary, just as the Assumption is the penultimate decade. The Assumption and the Coronation were both prayed by millions of Catholics for many centuries before the Assumption was defined on November 1st, 1950 by Pope Pius XII. Can we even pause to suppose that definition had nothing to do with the Fatima apparitions?
I should hope not!