Into the Wild Chapters 10-14

Some readers take great exception with Krakauer's inclusion / interruption of his investigation into Christopher McCandless' life to tell readers about his own travels to Alaska in his 20's.  
 
After reading chapter 14 answer the following:
 
1) Is it ethical for an author to literally insert themselves into the story 130 pages in?  (This isn't a story about the author. The author never met his subject. The author also didn't establish that this would be the way the story would be told earlier.) Perhaps it is ethical in other stories, but not this one...
If you make such a distinction (that is okay sometimes, but not others) what is the distinction? 
 
2) Is Krakauer's interruption helpful? What does it offer us that we (the general reader) would not otherwise have and need?  Does it help us view McCandless' decisions and actions more or less fairly? More or less objectively / subjectively?  Putting yourself in the author's shoes, why is this addition necessary? Make sure to be specific here and use at least 2 quotes. 
 
3) Lastly, did you find this element surprising?  Krakauer has used "I" a few times and referred to himself when discussing a few of his interviews, but nothing to this extent.  Do you feel like it slows the momentum of the McCandless story? If you were writing would you have done something like this (if you had a relevant story to share?)