On August 3, Robert Curry wrote a rebuttal, "Defending the Founders and the (American) Enlightenment," to my commentary "Modernity and the Secularization of Reason."  I'd like to answer by making some additional points to back up my original premise.

Rationalism was a way of thinking and viewing the world that grew out of the scientific revolutions.  Its developments and discoveries focused on the material world, inquiring into material truth that excluded spiritual truth and pushing aside the Christian worldview.  It doesn't explicitly reject the metaphysical and transcendental, but it clearly has no room for it.  This in turn led to the philosophies rooted in materialism of the rationalists (Descartes, Leibniz, Spinoza), empiricists (Locke, Bacon, Berkeley), the idealists (Kant, Hegel, Marx), and eventually to the existentialists (Heidegger, Nietzsche) and the pragmatists and positivists (Dewey, Comte), all of whom laid the foundations of modernity.

The long-term effect of the Enlightenment was to de-Christianize the world by shifting the focus from the eternal and transcendental to the temporal here-and-now.  The result has been what Martin Heidegger called "everydayness," where everyone has become immersed in the material world and distracted by the "newness" offered up by materialism.

Unquestionably, the Founding Fathers created the best political system the world has ever known.  Where the Founders synthesized the best of Enlightenment philosophers and their writings, the instigators of the French and Russian revolutions synthesized the worst elements in seeking to create a secular utopia.  This was also no doubt the goal of Hitler's Thousand-Year Reich for Germany as well as Lenin's Worker's Paradise for Russia.  So where the American Revolution (and Enlightenment) went in one direction, the French and Russian Revolutions went in another, but it cannot be disputed that the ideas of democratic republicanism, fascism, and communism emanated from the same philosophical roots, as I discussed in my commentary.

All three political systems existed under the umbrella of Western civilization and philosophy.  They certainly didn't grow and evolve out of Eastern, Islamic, or sub-Saharan thought.  Democratic republicanism eventually won the competition among the various iterations of Western political philosophies and ideologies.  What were World Wars I and II and the Korean and Vietnam Wars but that competition played out in the violent convulsions and confrontation of competing ideologies for political hegemony, all based on various versions of the same Western philosophy?  The same can be said about the Cold War between the United States and Soviet Russia.

In that respect, they all are rooted in the same philosophical soil.  But one implemented a governing system that provides the most freedom possible while recognizing and given the existing limitations to man's moral standing while the other two implemented political systems that limited man's freedom with zero moral standing.

The common thread from Descartes to Nietzsche (especially Nietzsche, since he famously declared the death of God and was known to be Hitler's favorite philosopher) and where all of the foundational philosophers of modernity went wrong is that they all failed to integrate a religious metaphysical moral order and instead substituted a morally neutral reason based on the materialism of the physical world, because the reason that developed out of their writings was morally neutral or inverted (Nietzsche's observation).

Although most of the Founders were either Christian or Deists, that doesn't discount the fact that they failed to be more precise and clear in integrating a moral order based on Christian values (despite their pronouncements to the contrary) into the Constitution.  The fascists and communists wanted nothing to do with Christianity and tried to destroy it, as those systems wanted to quash any challenges to their moral authority.

Unfortunately, secular humanism, the worldview rooted in materialism, was the outcome of the morally neutral reason developed by the writings of the philosophers of the Enlightenment through the early 20th century, and it branched out into a myriad of political systems, including fascism and communism, which does indeed make them, if not first cousins to democratic republicanism, then not so distant relatives.