Pontifications carries a fascinating archive on gnosticism in contemporary Christianity; Al Kimel's efforts at diagnosing the current unpleasantness in ECUSA led him to consolidate a rather rich series of ruminations that frighteningly come close to being right, in my opinion.
Summarizing Kimel's point with crude, reductive brevity, he claims we Americans are raised in a culture that celebrates self-actualization as ultimate (my category). For we are pulled by the prevailing cultural stew of modern America to presume an identification between God or Being and our individual selves. Thus, we seek above all to get in touch with ourselves, to purify ourselves in the sense of turning away from the messy concrete world to attend to the inner me, which for all its frustrations in the outer, material world is, taken in itself, clean, clear, and divine or at least spiritual (see this post of his, for example).
While he has most definitely identified a real phenomenon here, I have to take issue with his diagnosis. Gnosticism is predated by nondualist Hinduism, for example, which sounds very much like what he describes, with (for our purposes) irrelevant differences: that is, again crudely, deeper than the merely apparent phenomenal self is a single real Self, immutable and immaterial, and our salvation comes with the mystical realization of this great Truth. And gnosticism is followed by, for instance, Hegelian Absolute Idealism, in which the attainment of absolute knowledge functions like the Hindu mystic's realization, though in a weaker sense. In other words, gnosticism is one among many instances of "something" that manifests itself variously but repeatedly among us--I presume, an error of moral consequence we cannot seem to avoid, something incompatible with Christian belief and practice.
What is the something for which gnosticism, nondualism, and idealism are masks? A disposition to displace God as the center and put ourselves in His place--the kind of thing traditionally referred to by "the Fall" and "original sin", described in different terms (but still described) in the '79 BCP Catechism under "Human Nature". We are "naturally" (nature in a deranged sense) self-centered in this way, and our psychological egoism is the "true" Face of the selves we hold dear and desire to preserve. Gnosticism is just a mask worn by the Face.
We do not realize how dangerous this mask-seeking, debased Face really is; CF Allison has a good pamphlet from Forward Movement addressing the danger. The Face seeks closure, separation from the reforming power of God (aka God's love) that would begin the death or burial of the Face in its debased form (which it takes as true) with the sacrament of Baptism. Kierkegaard, in a brilliant move, identifies the successfully closed-off self with the Demonic: in our natural state we strive to emulate those vicious Powers for all we know possibly already beyond redemption--one death not being enough for us. Of course most of us do not know that destination under quite that description--but this sort of destabilizing ignorance is precisely what follows on separation from faith.
In contemporary Anglican Modernism, I tentatively believe the Face wears a form of Idealism as its mask, going in its latest iteration by the name "panentheism"; I'm influenced by a recent reading of "The Panther and the Hind" in that judgement; caveat emptor. Backing that up will take some work, which I do not claim to have finished yet--hopefully soon.