I suppose the answer to this question has to do with perspective, circumstance, and moral values. After Rat Kiley is gone, Bobby Jorgensen takes his place as the medic; however, Jorgensen is green and his fear is evident in everything that he does. Because O'Brien has been in the war for some time, he does not really remember the time when he was green and thus cannot sympathize with Jorgensen. Plus, there really is no room for this type of sympathy on the battlefield. Jorgensen has a job to do just like everyone else, and because he botches the job, O'Brien's wound becomes infected and O'Brien nearly loses his life once from shock and again from near gangrene. O'Brien feels a sense of hatred for Jorgensen, and this prompts him to want to take revenge on Jorgensen. The man nearly cost O'Brien his life, so O'Brien has cause, but the desire for revenge does consume O'Brien in an unhealthy way. Jorgensen thus becomes a scapegoat for O'Brien's deep-seated hatred of the war. O'Brien's feelings cannot be simplified into a matter of right vs. wrong because his perspective, circumstance, and belief is what is morally "right" are different from that of the outsider-looking-in.