What then is an "intimist piety" which the Holy Father describes as heresy?
I found this on the internet:
Anti-Marian Forms of Spirituality
Not all expressions of Marian devotion and "Marian spirituality" are truly and authentically Marian. There are too many well-intentioned Christians for whom the mere mention of Mary’s name serves as a cover for pious exaggerations, theological reductionism, and psycho-spiritual projections. Authentic Christian spirituality, which always has an engrained Marian dimension, proceeds from true faith, as Lumen Gentium reminds us, faith "by which we are led to recognize the excellence of the mother of God."75 Being even more specific, Marialis Cultus speaks of attitudes of piety which are incorrect,76 because they are "not in harmony with the Catholic faith and therefore must have no place in Catholic worship."77 This exhortation seems to be all the more pressing as many devotional practices of the past, some of which gave way to devotional deviations mentioned in Lumen Gentiumand Marialis Cultus, have been retrieved and are being once again practiced by many of the faithful, with spiritual profit. Rather than ostracizing specific Marian devotions, we would like to pinpoint some of the more current anti-Marian attitudes which lead to the misuse or misinterpretation of Marian devotion and spirituality.
This attitude mobilizes Mary as doomsday prophet and inspirer of fear and trembling. We all have need for some motherly exhortation and sisterly warning in the face of the moral and spiritual challenges of our lives. And, as we know, the fear of God is to be counted among the Christian virtues. By unilaterally and exclusively projecting the image of the Deus tremendus, apocalypticism demeans the Christian notion of love, which is mercy, and negates the reality and challenge of the Incarnation. This approach diminishes the figure of Mary by depriving her of an essential dimension. Mary is the mother of Incarnation, of loving presence to the world, and, therefore, an active agent of its transformation in Christ; that is, she is Mater rerum recreatarum and no doomsday sibyl.
Too much of Marian devotion is built on Mary’s role as Dea ex machina, and is linked to para-psychological realities such as special fragrances, weeping statues and rosaries turning golden. This is not a hidden or indirect criticism of apparitions and miraculous phenomena. But, indirectly at least, esoterism suggests an end to faith and the imminent dawn of beatific vision. Mary makes it possible. Instead of being a corollary to messages of conversion, prayer, and, in general, spiritual hardship, Marian esoterism reduces eschatology to the present and promises immediate spiritual satisfaction. Sensationalism, as esoterism is called in secular terms, favors spiritual consumerism and attributes to Mary magical power. Many related examples could be given; one of them deals with the almost magical and superstitious way in which the consecration of Russia to the Immaculate Heart of Mary is promoted.
There exists a certain tendency in Marian devotion and spirituality toward intimist or "privatistic" expressions of affection for Mary. "Marian spirituality" was never meant to become an "ivory tower" for Mary’s devotees. Although contemporary spirituality puts emphasis on therapeutic concerns for a world in need of healing, Mary is not simply the gatherer, offering her followers the protection and warmth of her maternal womb. An orientation to action and apostolic endeavor are an integral part of "Marian spirituality." Being disciple and associate in Christ’s salvific work, Mary is also a "sender," involving her followers in her mission of being mother of the Church and of all humanity.