McCandless' sister Carine recently wrote her own book, The Wild Truth, in which she describes the savage beatings her violent and alcoholic father dealt both her and Chris, and how their mother did nothing to stop this. Walt McCandless would force the two siblings down side by side, and beat them with his belt. She describes the "look of sadistic pleasure that lit up my father's eyes and his terrifying smile -- like an addict in the climax of his high." Carine had already shared this information with Krakauer in the 1990s but asked that he keep it off the record. Krakauer obliged, though he couldn't resist dropping in several subtle hints about an "overbearing" father.
Once you know that, the whole movie radically changes its tone. Every scene where McCandless is trying to opt out of society and refuses to keep in touch with his family becomes an abused kid running away so that nobody can hurt him again. By leaving that bit out, Christopher comes across as kind of a dick for leaving his parents worrying while he traveled the country, having a blast.
Well, except for this part..