The general reaction to Krakauer's article in Outside magazine is one of hostility towards Christopher McCandless. The consensus seems to be that Chris was, at best, a romantic fool, and at worst, a deeply irresponsible nihilist running away from the world and all its problems.
Krakauer defends McCandless by placing him firmly in a long tradition of American outdoorsmen, thus trying to persuade his critics that there was nothing particularly strange or out of the ordinary about his adventures in the Alaskan wilderness. By establishing parallels with explorers of the past, Krakauer aims to deepen his readers' understanding of Chris McCandless and perhaps generate some empathy as to his motives for embarking on his long, and ultimately tragic, journey.
Placing all this information in the middle of the book helps us gain a better understanding of Chris and what made him tick. The previous chapters largely take the form of narrative, providing us with details of Chris's family background and his subsequent journey into the wild. In the chapter prior to Krakauer's defense of McCandless, we see Chris indulging in selfish, irresponsible behavior where he alienates and emotionally hurts people he meets on his travels, such as the Vietnam veteran, Ronald Franz. Krakauer clearly feels it important at this crucial juncture to deal with some of the inevitable criticisms that will arise from many of his readers. As we've already seen, he does this by placing Chris's actions in a much wider historical context.