As part of him gaining refuge in horizon he had to become a test pilot of the COG and is under strict orders that if he intends to do anything that would jeopardize the mission (like physically maiming or killing any human) he will be sent to the nearest embassy. Plus I figured that it would add some good dynamics to have a human hating robot on the same team as a self righteous human. By the way that's part of what made me interested was reading Chie...that type of character is always my favorite in animes