The author is addressing the perception of Sparta as it exists in popular culture today. Which is to say - the perception that is fueled by movies like 300, and the military culture that adopted that perception to glorify itself by proxy. Because of that, the vast majority of people are not aware that Spartans were a tiny minority of the residents of Sparta (the state), or that most residents were slaves. If you do, great - but your assertion that the article "does not improve the reader's knowledge" is not grounded in reality.