Frustration period.
Four deployments, one head injury, trying to protect a bunch of dark age savages that hate him, commanded by civilian leaders that hate him as much as the dark age savages that he was trying to protect, his close friend has his leg blown off the day before by the dark age savages he is trying to protect.
I would say frustration with the rules of engagement is just one of the components.
I also say if he is found guilty and his sentence is more than say 50 lashes with a wet noodle, we should raise holy hell. More hell than the OWS mob ever dreamed of raising.