To answer this question, a reader needs to understand Finny's character and personality. Finny is athletic, playful, sarcastic, young, likes to challenge authority in a fun way, and he's not serious because he always wants to have fun. He is a typical 16 year old boy. But like many teens, he is too inexperienced with life to completely grasp huge, world-wide events that don't seem close to home for him. Hence, the war seems fake because it's not in his backyard. However, he is not so much in denial that he doesn't really know deep down that there is a global war on because he admits it to his best friend Gene during their last conversation. For as much as his young brain can comprehend, he doesn't want to be left out of the war because he does value everything that fighting the war stood for. It seems for Finny, that if he can tackle any issue as if it were a game, he could figure out how to come off conqueror because he always wins in competition.