In Into the Wild, why did Chris McCandless try to evade all emotional connections with people?
That is a question that does not have a certain answer; the reader must simply take what information he is given about Chris and draw his own conclusions. Chris was raised by parents who were far from perfect. He felt greatly wronged by them and was apparently felt so hurt and betrayed by them that he allowed his emotional injuries to push him away from being able to trust and have faith in his fellow man. In general, Chris felt that, as a whole, society is wrong in its approach to life; he felt that people should live free of the constraints and desires (material possessions, status, etc.) that most people subject themselves to. Basically, he felt that there was little or no truth in most people and their lives, so he did not wish to subject himself to what he felt was wrong.
The relative emotional-void Chris felt in his relationship with his parents certainly shaped his interactions with the world and the people in it he met. I'm not sure that I would say that Chris chose to evade all such emotional relationships with others; he certainly, however, was weary of such relationships and guarded himself against them. One reason might be his desire to avoid the hurt and pain that Chris associated with such relationships and to spare others such pain as well. Chris was also very cognizant of maintaining the lifestyle and freedom that allowed him to pick up and move on a moment's notice. Relationships that involved emotional connections with people would have made this more difficult for Chris, especially because of his own past.