In this article, I try to show that although the religious and intellectual movements now known as “Reformation” introduced potentially “revolutionary” ideas, even in the realm of political thinking and action, no revolution did actually take place, not least because of the victory of a “normalization impulse”, so to speak. After considering (only) two amongst the most innovative of those ideas, I briefly address the socalled “Radical Reformation”, moving thereafter to a discussion of Stefan Zweig’s Castellio gegen Calvin (1936), in which the Author tries to show the ambivalent character of the Reformation and its ideas – what I have called the “dark side” of the Reformation –, especially when it comes to the issue of the exercise of power, dangerously shifting from (at least potential) revolution to authoritarianism and even tyranny.