What's its purpose?

After reading the chapters "Enemies" and "Friends", I'm not really sure what their purpose in this book was. Maybe I do not know the ultimate reason for O' Brien writing this book yet, but they just seemed a little random. A guess that I have is that it really shows how the Vietnam war just made people a little cookoo and that just made them do crazy things. For example, when Strunk broke his own nose so that him and Jensen were even, (even when to Jensen they pretty much were) that just seemed a little on the crazy side. The war makes the people paranoid about everything. When you get paranoid about someone in your own troop, however, I'm sure that's just going to make that person a little insane. So maybe O' Brien put these 2 chapters in there to show how psychologically straining the war could be. But I am still uncertain.