Trying to communicate this important material [about the Ecumenical Councils] led me to ask the question, "What happens to someone who follows heretical teachings?" It became quickly and readily apparent how cruel heretical teachings are and how prevalent the heresies are in contemporary times. Victims of these teachings have been encouraged either to escape the world and their basic humanity into some form of flight and death or to use their religion to undergird and isolate further their own self-centered self from the need to be loved and to love.
We are susceptible to heretical teachings because, in one form or another, they nurture and reflect the way we would have it be rather than the way God has provided, which is infinitely better for us. As they lead us into the blind alleys of self-indulgence and escape from life, 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.
The conviction that heresy is cruel has given me a growing awe of and respect for orthodoxy. Unlike many contemporary scholars who seem increasingly to view these classical conciliar statements as irrelevant to the concerns of modern times, or worse, as impediments to be disregarded or obstacles to be overcome, I am convinced that seldom have these guidelines been more relevant than they are today. Neither ignorance of the heresies nor belief in their irrelevance can guard against making the same mistakes. Scarcely any ancient heresy can be found that does not have a modern expression; scarcely is there a modern heresy that we have not seen before.
Some argue that we have now reached a point in education, evolution, democracy, science, and spiritual maturity at which these ancient and classical formularies are rendered irrelevant. On the contrary, it is my conviction that not since the age of the councils have we needed them more urgently. All modern or contemporary attempts to resolve the ancient dilemmas are rarely if ever an improvement on those of Nicaea or Chalcedon. In fact, most of these attempts appear to be only slightly disguised version of the ancient heresies, and are frequently set forth without any attempt to deal with the original reason for their rejection.
~ C. FitzSimons Allison, The Cruelty of Heresy: An Affirmation of Christian Orthodoxy (1994)