It does not make sense to blame Christianity for the downfall of the West; the real story is more nuanced.
Christianity was taken up by the rising Left as a means of spreading individualism. Any religion where the choice of the individual to partake is considered a complete introduction to the depth of the faith will naturally become a vehicle for projection, which is why the Catholic church continued the Rabbinical tradition of isolating scholarship to those who had already demonstrated prowess.
This elitist viewpoint is called esotericism, meaning that it is based on mysteries and not memorization. Topics are seen through a qualitative lens that views them as having depth, such that their initial summary in language is a gateway to a series of cause-effect relationships and their implications. The more one learns, the more there is to learn.
Esotericism also relies on logical collisions to determine boundaries, instead of categories. The opposite of esotericism, exotericism, teaches through categories, where a single detail stands for the whole and is presumed to impart that characteristic uniformly to all objects within the category. This provides an easier method of thinking, thus a more popular one.
Logical boundaries on the other hand occur when the thinker looks into the depth of an idea through its extension to a logical extreme and the implications of that, in infinite cycle. This resembles the thinking of a chess player, looking ahead as many moves as possible by accounting for every potential move by the other player. In this view, objects have many details, and it is important to take the interaction of objects with other objects on a case-by-case basis, seeing how the details collide and coincide to determine the nature of those objects. This gives humans less perceived power through an easy method of thinking, but is more accurate.
Christianity suffered weakness because it was based on the Word. The Word first appears in the creation of the world, and then extends as a theme in the Bible through people accepting word tokens as literal truth, without having depth to work through, implying an equality of all people in understanding. This approach lends itself to propaganda.
At first this was an advantage to Christianity. It could induct and unite huge groups of people quickly, which is why the pagan faiths faded away; they simply could not compete. As a theology derived mostly from the Greeks, early Christianity conveyed a strong Indo-European philosophy. But its strengths were also its weaknesses, making it easy to take over from within.
Some claim the rise of Protestantism was part of this process, but it may have been resistance to the effect that having the Bible widely available in lay languages was having within Catholicism.
This upheaval resurrected an old conflict that had lain dormant throughout the middle ages. Before the preceding millennial turn, Throne and Alter had been in conflict as the monarchies of Europe found themselves needing allies during war, and in addition to domestic splintered politics, having to placate special interest groups. The Church too often played as a self-interested party.
With the middle ages, this condition was suspended as some parity was reached and Church and monarchy could work together. However, this was short-lived, as Christianity proliferated into different cults with the rise of mass distribution of the Bible, in part pre-dating the printing press as the supply of hand-copied Bibles accumulated over the years.
At that point, a new internal religious conflict began, one that would eventually give rise to the nascent Leftism of The Enlightenment™ and the Romantic period:
In Cavanaughâ€™s The Myth of Religious Violence, Cavanaugh presents a thesis which is radically at odds with received wisdom concerning the origin of the secular state. Citing the examples of Baruch Spinoza,Thomas Hobbes and John Locke who presented religious division[ii] as the cause of the conflicts of the period, he notes that this narrative provided:
…the backdrop for much of the Enlightenmentâ€™s critique of religion. There developed a grand narrative in Enlightenment historiography â€” typified by Edward Gibbon and Voltaire â€” that saw the wars of religion as the last gasp of medieval barbarism and fanaticism before the darkness was dispelled.
More modern liberal thinkers have subsequently traced the birth of liberalism to the so-called religious conflicts of this period, with Cavanaugh citing Quintin Skinner, Jeffrey Stout, Judith Shklar and John Rawls as exemplifying this narrative.
When a conflict of this sort arises, more likely what happens is that one party was neutralized, allowing some event to take place. The “fanaticism” of the medieval era was an attempt to retain balance between different power structures within civilization, because they remembered what happened to Athens, Rome and pre-medieval Europe.
If instead of viewing the religious wars as a conflict between religion and anti-religion, but a struggle for power within civilization, we see that an unnamed third force won: egalitarianism.
As Cavanaugh takes pains to point out, the institutional changes which were supposed to have been ushered in as a result of the religious conflicts actually presaged them. To bolster his argument he provides ample examples of conflict occurring between states with the same denominations, as well as collaboration between differing denominations. The most trenchant observation is provided by the example of Martin Luther:
As Richard Dunn points out, â€œCharles Vâ€™s soldiers sacked Rome, not Wittenberg, in 1527, and when the papacy belatedly sponsored a reform program, both the Habsburgs and the Valois refused to endorse much of it, rejecting especially those Trentine decrees which encroached on their sovereign authority.â€ The wars of the 1520s were part of the ongoing struggle between the pope and the emperor for control over Italy and over the church in German territories.
In other words, while the Church struggled against the kings, someone else took power. This became The Enlightenment,™ which had fortunate timing in that it caught the early years of the industrial revolution within a century and, because it perfectly justified unlimited growth and tragedy of the commons, replaced religion with the new mythos of the individual.
For this reason, “Christianity caused Leftism” is too simple of an analysis, just like “Christianity is the root of Western Civilization.” The root of Western Civilization is its people, but they depend on quality leadership from the aristocracy in order to be effective. We removed that, and now we are removing our own people so that it can never be reborn.