My undergraduate degree is in Physics, and along with this I have spent several years studying Cosmology on the side. When Hitchens compares Astronomy to Astrology, he reveals the doltish but common habit of reaching for the reductio ad absurdum bag of argumentation in order to stifle reasonable dialogue. As well, he dismisses the relevance of teaching the history of competitive scientific theories in a way that reveals his absence of scientific knowledge. In my reading of Hitchens - I find that he has a regular habit of revealing such weaknesses. In areas of scientific study, where the research is highly dependent upon hypothesis and empiricism, it is most common to give a historical and comparative analysis of competing scientific theories. The study of Cosmology is an excellent example of this. One might wish to assume that the world of Cosmology is populated with scientists who are in perfect agreement over the subjects of dark matter, the constancy of the gravitational force, or say, the determination of cosmological distances using cepheid stars etc., but this is simply not the case. Thus, science textbooks which reveal such scientific hypotheses and theories will normally do so with a comparative analysis of competing views throughout history. It is the most honest way of doing science. Those who fear such open competition of thought, and who seek to stifle any opposition, are pursuing something other than science by definition.