Memes

You're looking more at what the capitalists used to overthrow the aristocracy while entrenching their own rule here. Marx was an atheist, and built on the labor theory of value, for example. However, these liberal values were made with a mechanistic materialist outlook, not a dialectical materialist outlook, and as such could not actually stand for proletarian liberation.

Marxism is secular, has the labor theory of value, etc, but not because Marx was a staunch liberal and believed capitalism to not be capable of fulfilling these. Rather, he built upon what was already created to build new ideology.