Despite Chris's real intention, to find himself and return home, his attitudes and methods were deliberately isolationist; he refused shows of affection from friends and did not contact his family, causing them great pain. However, he did keep in contact with friends he met on the road, usually through postcards. Chris, because of his quest for self-understanding, deliberately avoided anything that might lead to "settling down," instead preferring to pass through people's lives. This is seen most clearly in his interactions with Ron Franz, who became entirely enamored with Chris, and had his offer of deeper friendship rebuffed.
At one point Franz dared to make a special request of McCandless. "My mother was an only child," he explains. "So was my father. And I was their only child. Now that my own boy's dead, I'm the end of the line. When I'm gone, my family will be finished, gone forever. So I asked [Chris] if I could adopt him, if he would be my grandson."
McCandless, uncomfortable with the request, dodged the question: "We'll talk about it when I get back from Alaska, Ron."
(Krakauer, Into the Wild, amazon.com)
This shows how Chris avoided getting bogged down in personal relationships; while he valued the company of others, he didn't want to be tied to them.
The other issue, that of "isolating himself from common sense," is harder to answer. While Chris certainly made many mistakes, some of which led to his death, it's hard to say if the cause was simply Chris not thinking about consequences, or if he truly thought he was capable of living in the wilderness. In fact, Chris did survive well for several months, and it was only his lack of woodcraft knowledge that eventually tripped him up. While it could be said that Chris's refusal -- or misunderstanding -- to properly prepare himself for the Alaskan wilderness lacked common sense, it could also be said that Chris wanted to experience the natural world without the cynicism of knowledge. This may or may not be a negative. In the book, Krakauer talks through various arguments, and never really reaches a definitive conclusion.