Heresies wouldn't get very far without being plausible and attractive. There must be some advantage in embracing heresy, something appealing to the mind, the heart, the will, the lifestyle, that makes them worth believing.
I suspect that each particular form of heresy and false teaching has elements that supply the motives for embracing them and rejecting orthodoxy. It is part of our task to figure out what these are in each particular case. Sometimes the appeal is crass, as in the health and wealth gospel, at other times it is more sophisticated.
Almost ten years ago I came across The Cruelty of Heresy by Fitzsimons Allison. Strangely enough it was in the reduced section of a health and wealth bookstore, glinting like a jewel in a dung heap. It has been the most stimulating book that I have read on the subject. Here's what he has to say:
We are susceptible to heretical teachings because, in one form or another, they nurture and reflect the way we would have it be rather then the way God has provided...heresies pander to the most unworthy tendencies of the human heart. It is astonishing how little attention has been given to these two aspects of heresy: its cruelty and its pandering to sin. (p. 17)Fitzsimons Allison applies this insight to adoptionism and docetism. Adoptionism imagines a Christ who is like us only much more successful. This "Jesus" is top of the class and graduates to become the Son of God. This panders to our self-righteous, to our thirst to achieve our own salvation. Either that or, if we have a true sense of our own sinfulness, this "Jesus" crushes us by his unattainable achievements.
The docetic Christ was not truly a man but only appeared to be. This is theological escapism at its worst. This Christ matches our desire to flee from the trappings, reality, earthiness, and nitty gritty of life. Our humanity is simply too sinful for this spiritual Christ to partake of. Not only is this a bogus Christology it is also a damning verdict on the very goodness of creation.
This insight can help us understand why heresies spread. There is a saying that "heresies are the unpaid debts of the church." In other words, the reason for heresies should be laid at the door of the church that hasn't done its job properly. Perhaps it was a failure to teach the whole counsel of God, or a perceived harshness and lovelessness on the part of the orthodox that has driven people to buy into error.
This is sometimes given as a reason why people from fundamentalist backgrounds are attracted to Emergent church thinking. It certainly can lead to a lot of hand-wringing on the part of those who haven't deviated from the truth ("it is all our fault that those sincere seekers after truth have fallen into the pit of error"). Perhaps in some cases this holds true as a contributing factor. However, as a general law it should be discarded.
There is no logical reason why a reaction against a narrow or harsh orthodoxy automatically leads to the embracing of heterodox views (just as there is no justification for ungodly reactions if we are treated in ungodly ways). This is a false move. Heresies give us what we want.
The attraction of the psuedo-spirituality of the Colossian heretics and the legalism of the Judaizers in Galatia were not to be laid at Paul's feet as if his preaching (or that of Epaphras) was to blame. In Colosse the heady brew of legalism and mysticism that offered genuine fullness had "an appearance of wisdom" but was of "no value" (Col. 2:23). Mystical and ascetic channels to communion with God fitted better with the aspirations of the fallen human heart. Paul offered union with Christ and his finshed work instead. The Judaizers offered the road to self-righteousness and the escape route from persecution (Gal. 6:11).