Strauss offended—sometimes zestfully—academic orthodoxy’s easily offended prejudices.
In article after article and book after book, he argued that contemporary scholars were enthralled to “historicism” and “positivism.” Historicism holds that ideas and principles are nothing more than an expression of their time and cannot transcend the historical era in which they arose. Positivism decrees that the natural sciences offer the only legitimate form of knowledge and adds that since the natural sciences cannot distinguish between good and evil, all value judgments are subjective. (Postmodernism radicalized this sensibility by denying that science itself yielded objective knowledge.)
In much of the academy, historicism and positivism came to be taken as self-evident truths. That both imply moral relativism, which means that there is no rational basis for judgments about right and wrong, was seen by many of Strauss’s colleagues in the university world as an important contribution to progress.
Left-liberals regarded the supposed discovery of moral relativism as a blessing because they believed it bolstered pluralism and toleration. If there is no truth about the moral life, then custom and tradition lack authority, individuals are freer than ever to make their own choices, and society can dedicate itself to letting a thousand flowers bloom.
Strauss trenchantly argued, however, that the principles of freedom depend on the conviction that human beings are by nature—that is, universally, objectively, and rationally—free and equal. If instead all moral judgments are equal, if no political principle is more true than any other, then there is no rational objection to might asserting its right and the ruthless grabbing all they can.