Graff is undoubtedly manipulative. He intentionally drives the other kids away from Ender to isolate him, he convinces Ender that his fight against the Buggers is a simulation, and he frequently plays emotional games with the young boy. He also freely uses children in order to win the war, and does not hesitate to arm Ender with the weaponry to destroy an entire planet. All of this aside, I still believe that Graff is not selfishly motivated. He shows no signs of enjoying any of it. He is simply a military man forced to take extreme measures. All of these actions would be horrible in other circumstances, but consider the stakes. Graff is tasked with training leaders who can potentially save the entire human race. His actions harm Ender and the other children, but Graff believes this is crucial to winning the war. Graff has devoted his life to keeping others safe. In war massive sacrifices are often made. Ender unknowingly allows thousands to die in his assault of the Bugger planet. Graff is merely doing what he believes he needs to in order to preserve human life. Ender must be ready. The stakes are too high for men like Graff to put one boy's happiness over the success of the mission. He might not be justified, but his motivations are good.