Postmodernism is a toolset, and the thinkers who are bunched together under its umbrella, frequently unwillingly, point out the issues with late rationalist epistemology.
That is, the postmodernists are responsible for attempting to show the rest of the people that the boat has severe cracks. Fascists and right wing authoritarianism has already been exploiting the cracks forever.
Blaming postmodernism for anything is laughable. It’s not a cause, it’s a series of well informed observations.