Is the Establishment Clause a form of censorship?

One of the central parts of Michael Egnor’s argument (if such it can be called) for sneaking religion into science classes in violation of the First Amendment is to argue that restricting science classes to science is a form of censorship: that is, that the prohibition on putting a government imprimatur on a religious claim (i.e., Establishment Clause) is a violation of the principle of free speech.