Yeah, and even though you might expect people to be conscripted for the Empire, and therefore more or less innocent, the only information given in the films is voluntary service. Luke wants to join the Imperial Academy (to jump ship for the Rebellion, as we learn in the deleted Biggs scenes), but his Uncle says no way. So, it was a choice Luke made on his own, and in the end he didn't even end up joining because his guardian forbid him. That makes the Death Star personell fair game. They were serving as the command crew in what is ultimately a habitable weapon of mass destruction. Mass destruction doesn't even begin to describe the level of weapon they were crew members of. It's essentially like bombing a tank and killing the tank crew inside, only the tank that the Empire built required the manpower of a whole space station. But nonetheless, the world's biggest tank it was.