"I am not a happy man, Ender. Humanity does not ask us to be happy. It merely asks us to be brilliant on its behalf. Survival first, then happiness as we can manage it."
Mazer Rackham is telling his version of a philosophy similar to Graff's, but the difference is that he allows for the possibility of people playing roles as more than just tools. Rackham believes that people are primarily tools, because survival is foremost, but then afterwards they may be concerned with finding some sort of happiness. Ender was not happy with Graff's philosophy, but Rackham's is one he can live with. People must make sacrifices, that is true, but they also must have a chance to do something for themselves.