Why were many of the Alaskans who wrote letters about McCandless so critical of him? Why were they critical of Krakauer?

In Jon Krakauer’s nonfiction book Into the Wild, Krakauer expands on a previously published feature article he’d written for Outside Magazine about McCandless. While the book may be highly regarded by some reviewers, others perceive the story as being something fictitiously constructed by Krakauer. The criticism of the author is related to the unreliability of the story, and although some of what is included is rooted in fact, there are many components that would be unverifiable.
According to some of the people living in Alaska—and perhaps most notably, park rangers—McCandless's actions and choices can most easily be classified as “[not] even particularly daring, just stupid, tragic and inconsiderate.”
Peter Christian is a park ranger who moved to the area around the same time as Chris McCandless and was also from the same area on the East Coast. He had similar desires to explore the uncharted wilderness terrain, but his whole approach to the adventure kept him alive. He is critical of the way McCandless went about pursuing “the free life in the Alaskan wild” and comments specifically on the lasting consequences.

Some like McCandless, show up in Alaska, unprepared, unskilled and unwilling to take the time to learn the skills they need to be successful. These quickly get in trouble and either die by bears, by drowning, by freezing or they are rescued by park rangers or other rescue personnel—but often, not before risking their lives and/or spending a lot of government money on helicopters and overtime.

It seems that the people who are/were so critical of the escapade were really just concerned with setting a precedent, too. The book and McCandless’s story on film are sort of glorified, whereas the reality of life in the wild is certainly not glamorous. The reality of life in the wild is raw, difficult, and challenging.
The concern, therefore, of Alaskans and those critical of the story was most likely related to the improbability of fully living off-grid and surviving. Plus, there would most likely be lasting impacts on the communities around the areas, where “mostly young men” would end up dying from being ill-prepared to seek this “wild freedom.”