We cannot explain why orthodoxy wins over heresy by appealing to the iron heel. If the Church ever crushed opposition, proponents of this view citing the relatively bloodless Inquisition and more sophisticated critics citing the crusade against the essentially anarchist Cathars, it is not the pattern. For example, over the Arians, who had full state support, orthodoxy prevailed through the martyrdom of the again-oppressed Christians. Against the lies of the Eastern bloc governments, Christianity flourished in defiance.
I do not say that Christian truth is and always has been oppressed — as ignored as it may be from time to time — nor do I attempt to justify the Inquisition, but rather I say that reality is not nearly so simple than the “iron heel” hypothesis.
To go farther we must define our terms: Orthodoxy translates as “right belief,” and so the opposed, heresy, is “wrong belief.” More specifically, heresy is “undue emphasis of a certain portion or aspect of doctrine at the expense of another.” Heresy is, essentially, deception. As with all lies — and all evil things — it begins with a truth and twists or inflames that truth beyond its proper portion. It is obsession, very soon paired with denial of ecclesial authority, and, I believe, motivated more by a desire for originality or worldly fame than for truth. On the simple level of falsehood, heresy is already grave matter.
This is why in labeling or not a thing as heresy the Church treads carefully. We cannot truthfully say that Church rebels at the City of Man but rather that She condemns the aspects intrinsically tied up with sin. We must also note that the Church does not call every new thing a heresy. In the words of Kreeft:
My position is no a priori prejudice against change in the Church. Many of the saints can and did call for changes in the Church.
As with all living things — life reflecting the Greatest Good — the Church grows and changes over time in Her accidents. The Church never changes in substance. In this way, the Eucharistic Body of Christ is much like the ecclesial Body of Christ. This is so obvious on a moment’s reflection that I am ashamed at not thinking of it before. As is Adoration, it is a great calling to meditate on the substance of the Church, and better still to have something to say about it, even if all we can muster is straw. What provokes us to meditation? Heresy.
Heresy is an evil thing, but from renouncing heresy comes a deeper understanding of revelation and our logically consistent traditions, passed on in ritual and constant teaching since apostolic times. Here, as always, we see that from evil comes a greater good. It’s almost Chestertonian: We encounter God by countering heresy.