Why did Krakauer interrupt the McCandless story with Chapters 8 and 9?

In Chapters Eight and Nine, Krakauer, for the first time, describes the other famous and infamous characters to whom McCandless is now often compared. Krakauer makes his own beliefs clear—that though McCandless shares some characteristics and behaviors with these men, the only one who is truly like him is Everett Ruess. Carl McCunn was more naïve, John Waterman was actually mentally insane, but Everett Ruess was, like McCandless, simply deeply in love with the land, very romantic, and passionate about living by his principles. These comparisons show that removing oneself from society and living riskily can be a symptom of insanity or stupidity, but it is not inherently so.

This in turn emphasizes the need to look deeply into something before passing judgment. Those who compare McCandless to John Waterman, for example, are doing so based on a few parallels, but a detailed study of either character very quickly shows that their motivations and behaviors were very different indeed. This highlights the purpose of Into the Wild itself, which is not just to tell an adventure story, but to study McCandless in the closest possible detail, so that is anyone is to pass judgment, it is at least with all the necessary information.