STEM has had many false theories (like the sun revolves around the earth). The virtue of STEM is when the facts contradict the theories, the theories get revised, even if the old guard has to die off before the corrected theory replaces it. With Marxism, however, the facts get re-written to conform to Marxism, rather than the other way around.
One of the beauties of the scientific method is it tests the predictions a theory makes. If the predictions come true, the theory is validated. If the predictions don't pan out, the theory is false.
A famous example is Einstein's Relativity theory predicted that gravity bends light. Einstein became world famous when decades later, this bending was observed.
Marxist theory also makes predictions, but none of those predictions pan out. This never discourages the critical thinkers in the humanities, which leaves me unimpressed with the critical thinking skills of it.