Complex sentence: As a self-described antitheist he regarded the concept of a god or supreme being as a totalitarian belief that destroys individual freedom, and argued that free expression and scientific discovery should replace religion as a means of teaching ethics and defining human civilization.
Split into simpler sentences: As a self-described antitheist he regarded the concept of a god or supreme being as a totalitarian belief that impeads individual freedom. He argued that free expression and scientific discovery should replace religion as a means of informing ethics and defining codes of conduct for human civilization.