Use history. Marxism failed in the soviet union, China, Cambodia, Venezuela, everywhere its been tried. Cultural Marxism is the same oppressor vs oppressed concept ascribed to culture. People are far too complex to be put in these neat categories that identity politics creates. Individual rights are the key. The power and freedom of the individual, and capitalism, are what has created the highest quality of life, for the most people, in the history of the world. Also remember, Marxism wants to dismantle and disrupt, which it is good at doing, but the mechanism that would create the "utopia" that Marxism describes, can't be articulated. It is supposed to "just happen" after the marxist revolution happens. It has never created a utopia and never will, it only destroys order.