Why did Auguste Comte reject Roman Catholicism and royalism?

Auguste Comte rejected the Roman Catholicism and royalism of his parents at an early age, largely due to the influence of the republicanism and skepticism that permeated France following the French Revolution.3

His rejection was rooted in his intellectual development and his quest for a new, stable social order in the wake of the revolutionary and Napoleonic periods. Comte came to view theology—including the supernaturalism of Christian traditions—as an outdated, imperfect mode of knowledge. He believed that human intellectual progress had moved beyond such stages toward a "positive" stage, where knowledge is based on empirical science and the discovery of natural laws.1

While he abandoned traditional religious and monarchical structures, Comte sought to replace the "void" left by waning Christian beliefs with a secularized spiritual order. He proposed a "religion of humanity" that utilized the hierarchy and discipline of the Roman Catholic Church as a structural model, but replaced its theology with a system guided by sociology and scientific planning.12