It's apparent that McCandless enjoys his friendship with Franz. Why does McCandless avoid the issue of 'adoption' when Franz brings it up?

Ronald Franz is the strongest example of someone who quickly becomes attached to McCandless. With Franz it is so extreme that he asks to adopt McCandless, and changes his lifestyle completely, following Chris’s advice. Yet this also, somewhat painfully, puts McCandless’s selfishness in stark relief—although he accepts a fair amount of help from Franz, he leaves him before too much can be expected from him, and McCandless’s death causes the old man to lose his strong faith in God, and to take up drinking again. This illuminates the actual costs of McCandless’s risky behavior, not just to himself but to those who care for him.