"the counterfactual in which postmodernist philosophy never came into being has less acceptance of those concepts"

Still needs unpacking. What does "never came into being" mean for a belief cluster with many components that predate the label by a long way? "If these beliefs didn't become popular, they wouldn't be popular" is kind of hard to argue against. "novel aspect X of postmodernism caused faster/more complete acceptance of the classical liberal values" could be an interesting debate, and I don't know of any X that's a slam dunk to be both new with postmodernism and important to "live and let live" as a societal attitude.