[mjp]

Not all Leftism is based on Marxism. Admittedly, varieties of Marxism are dominant, but it isn’t the sole foundation.

exactly, the 3 main worldviews of libtardism are marxism, secular humanism, and postmodernism.All 3 dispise Christianity.

[walford]

Secular Humanism and post-modernism are arguably related if not derived from each other. Which came first is a chicken-or-egg question.

All are forms of subjectivist Utopianism — which are rooted as far back as Plato. They all deny objective truth and values, believing instead that people can be made to conform to an arbitrary ideal of how they think things should be, which will work if enough people believe in it — as I explain in the OP.