I understand that we are not obligated to believe in apparitions, even those sanctioned by the Church.
However, there are Catholics who question the legitimacy of Fatima.
It is true: it is not binding on pain of sin to pay heed to the message of Our Lady of the Rosary at Fatima, as it is private revelation.
However, neither is it sinful to omit the Holy Rosary "every now and then" but it is no reason to do so, especially when it is self-serving sloth that motivates such disedifying "minimalism." As spiritual directors and the experience of many may testify, such an attitude ultimately and ineluctably leads to tepidity and even to a total abandoning of the cultivation of the interior life of grace and prayer.
Though the messages of Our Lady of the Rosary at Fatima constitute private revelation, the contents thereof are a wondrous epitome of the
depositum fidei and, by benign dispensation of Divine Providence, they were given particularly for the sake of those interior souls living in the twentieth and twenty-first centuries and who, despite the aberrations and disorder of the present age, would aspire to the heights of prayer and penance, especially and particularly by means of true devotion to the Blessed Virgin Mary.
I personally believe the message of Our Lady of the Rosary at Fatima is the spiritual doctrine of St. Louis-Marie de Montfort applied to the predicament of interior souls in the present ages. Fatima ultimately leads to total Consecration to Eternal Wisdom through Mary Most Holy, and this constitutes the most perfect renewal of our Baptismal vows. This would compel a soul earnestly endeavoring to cultivate the interior life to pay heed to Our Lady's message at Fatima.
The miracles at Fatima also oblige an interior soul to cease questioning the messages of Our Lady. Together with the miracle of the terpsichorean Sun, the most remarkable thing of Fatima (at least to me) is the manner in which sublime truths of dogmatic and moral theology are given in a celestial simplicity readily understood even by children, akin to the manner in which the sacred Evangelists recorded the life and words of Our Lord in the holy Gospel. Such a thing, impossible to imitate or artificialize, is (at least to me) one of the signs that Fatima is indeed beyond question.
This is why the faithful deem it rash, perilous, offensive to pious ears, and to the detriment of the spiritual maternity and mediation of the Blessed Virgin Mary, to question Fatima in a spirit of either minimalism or cynicism or rationalism; or consigning it to "the past" and "irrelevant" to us now.