Aoshi is quite a pitiful dude, but his case is easy to understand. All his life, he got ready for a battle that never happened. It also means he never got to experience the horrors of war first hand. He never had to make the really difficult decisions in the middle of a big fight. He's like a man who has been training himself at a gym, boxing ring, and shooting range, perhaps worked as a bouncer and read a bunch of books on warfare, and then fancies he's the perfect soldier for the WW3.