One of the personal philosophies that Chris adopted was to keep himself at an emotional-arm's-length from people he met; he saw personal relationships as materialistic as wealth and belongings. Even though he became close friends with many of the people who helped him during his journey, even mailing postcards and letters to reassure them of his safety, he refused to enter into any emotional relationships. This is seen most clearly in his friendship with Ron Franz, who became so fond of Chris that he asked to adopt him; Chris refused to make a decision, since he felt it would be restrictive.
McCandless was... relieved that he had again evaded the impending threat of human intimacy, of friendship, and all the messy emotional baggage that comeswith it.
...their burgeoning friendship also reminded him how lonely he'd been... When McCandless departed as suddenly as he'd arrived, Franz found himself deeply and unexpectedly hurt.
(Krakauer, Into the Wild, Amazon.com)
Franz felt both a personal connection to Chris, and a protective paternal connection; he wanted Chris to become a surrogate grandson, since he had none of his own. He felt so strongly affected by Chris's ideals that he became something of a recluse himself; he never got over Chris's death, renounced his religious faith, and died a few years later. Chris's refusal to make this deeper connection is also seen in his other friendships, where he partook of hospitality and continued correspondence, but never allowed himself to become emotionally attached.