They are both axiomatic systems that assume their premises.  This allows both to make facile deductions that are favorable to their respective views of the world.  This is similar to Christian theology. This gives both a "feel" that makes them more plausible to their target audiences. Marxism has the advantage in internal coherence.  Liberal and Neo-Liberal Economics have the advantage in direct appeal to the vanity and self interest of the wealthy.  When adopted by governments, political entities or social organizations each spends considerable effort delegitimizing any criticism of the assumptions, which is where all axiomatic systems are most vulnerable. IMHO, in the US the similarities in axiomatic structure between fundamentalist Christian theology and Neo-Liberal Economics rallies fundamentalists to the support of Neo-Liberal Economics when it's axioms are attacked.  I suspect they have come to view the "Invisible Hand" as the Left Hand of God.

As the Dutch said while fighting the Spanish: "It is not necessary to have hope in order to persevere."

Didn't Einstein also say "if experiment hadn't confirmed my theory I would have felt sorry for nature because my theory is correct"?

When the capital development of a country becomes a by-product of the activities of a casino, the job is likely to be ill-done. — John M. Keynes