A friend of mine related to me how some folks in a discussion he was having were insisting that anyone who does not believe Fatima is being unfaithful to the Blessed Mother. I wanted to take some moments to address this.
According to Vatican II Dei Verbum as quoted the Catechism #66, "no new public revelation is to be expected before the glorious manifestation of our Lord Jesus Christ." This means that with the death of the last apostle, revelation which is binding on all Christians ended. The Catechism goes on to say (#67), that private revelations — which is what Fatima and all other revelations since the death of St. John are — "do not belong to the deposit of faith", that is, that which must be believed by all Catholics. Pope Benedict XIV says: "It is not obligatory nor even possible to give them the assent of Catholic faith, but only of human faith, in conformity with the dictates of prudence, which presents them to us as probable and worthy of pious belief"(De canon., III, iiii, xxii, II). The conclusion is that no one is obliged to believe what a private revelation says, except perhaps the person to whom it was revealed.
But what if it is approved? "When the Church approves private revelations, she declares only that there is nothing in them contrary faith or good morals, and that they may be read without danger or even with profit; no obligation is thereby imposed on the faithful to believe them." (1917 Catholic Encyclopedia) So church approval does not mean that the revelation is divine and true, only that one may believe it without danger to one's faith.
This is not to say that there is anything wrong with private revelations, far from it; but they are just that, private, and they are icing on the cake, but they are not the cake itself. People are free to believe that Fatima is true or not true.
What about all the good fruits? Certainly, these are compelling, but everyone must ultimately use his or her own judgment.
It's entirely possible for a revelation that looks good to be a demonic deception. After all, Satan often masquerades as an "angel of light" (2 Cor 11:14). How else is Satan going to deceive the pious except by feeding something to them entirely in conformance with their beliefs? I know I've been deceived this way before, and it is not beyond belief that this happened to some very pious people with their private revelations. God sometimes even allows Satan to use the same manners of revelation that God himself uses. The net result is that it is impossible to tell for sure that a certain revelation is demonic or genuine until all things come to pass.
You may object, well, Fatima predicted World War II! Yes, it did, , but do you not think that Satan had a hand in World War II and wasn't planning it? And may I point out though that Russia isn't near to being converted in any reasonable sense of the word. Also the "era of peace" that is supposed to arrive before Lucia dies — well, she is pretty darn old so the era had better arrive faster than the conversion of Russia.
I think God often allows Satan to deceive us using supernatural revelations in order to purify us. Satan is betting that it will harm our faith when the revelation proves to be false. But God knows it will just purify us.
We ought not cling to private revelations in the sense of putting our faith in them. Our faith is not in private revelations but in Jesus Christ. Demons masquerading as angels of light do deceive the faithful, and it is no shame to be deceived. If a revelation brings us closer to faith in Christ, wonderful, but let our faith then rest on Christ in such a way that if the revelation is proven false, our faith does not turn false with it.
Whether you firmly believe in Fatima or have doubts, let's at least agree that our faith is in Jesus Christ and not in private revelations.

Huh? Fatima was in 1917, while WW I was already underway.
I think that Fatima was predicting WWII. I'm not one for private revelations myself. I tend to be a bit suspicious of them.
Should have gone with what I originally wrote! I thought it was WWI and then changed it. I'll edit the text.