In Kurt Vonnegut's novel Slaughterhouse-Five, Billy Pilgrim is caught in a time warp, making him shift back and forth without warning to different points in his life. (Those who want to read my thoughts on the 1972 film adaptation can go here.) Vonnegut uses this plot device in two ways: to tell a semi-autobiographical account of his experience as a POW in World War II, and to express his mechanistic outlook on life.
This isn't the kind of time travel where you can change your own past. Billy occasionally tells people around him about future events he has seen, and he appears to take this information into account when making choices. But there's a sense that he never tries to change anything. Thus, he gets on a plane he knows will crash, without even making a fuss about it, because "he didn't want to make a fool of himself" (p. 133). What would have happened if he had avoided the flight? The book never answers that question, and there's an underlying implication that he has no ability to avoid what he knows will happen.
As in most time travel stories, the reader had best not scrutinize the logic of the situation. If it is possible to possess information about one's future, then there is a potential for the events to turn out differently. Books like this may try to ignore that fact, but it is inescapable.
Vonnegut wants to argue that everything which happens in life is inevitable, including the choices one makes, and thus that even someone who sees the future cannot control his own choices. But this notion overlooks the crucial consideration that a part of decision-making involves the information that one possesses. How many decisions might you have done differently had you possessed more information about the outcome?
Later in the book, Billy finds himself inside a dome on Planet Tralfamadore, where he becomes an exhibit at some alien zoo. This situation is not meant to elicit horror. He has conversations with the alien scientists, and he isn't trapped, since he's still constantly moving back and forth to other points in his life. The aliens themselves are even more detached from the human time frame than Billy is, living as they do in the fourth dimension. Because they view life from outside of time itself, all events to them look like one big simultaneous blob. They "don't see humans as two-legged creatures.... They see them as great millipedes--'with babies' legs at one end and old people's legs at the other'" (p. 75). This situation naturally affects their entire outlook. As one Tralfamadorian explains to Billy, "Today we [have a peaceful planet]. On other days we have wars as horrible as any you've ever seen or read about. There isn't anything we can do about them, so we simply don't look at them. We ignore them. We spend eternity looking at pleasant moments" (p. 101). Vonnegut here seems to be hinting at the real message of his book: that our purpose in life should not be to control what happens (that being impossible), but to cherish the good moments.
Of course, this philosophy involves a denial of the concept of free will. Vonnegut has the alien insist, "I've visited thirty-one inhabited planets in the universe, and I have studied reports on one hundred more. Only on earth is there any talk of free will" (p. 74). The position that free will is so unnatural that an alien likely would be perplexed by it is a strange assumption, considering how vital the concept is in human society.
If you don't believe me, imagine the following scenario: a stranger begins hurling nasty insults at you. Naturally, you think, "What a jerk!" But how would your judgment of that person change if you knew he had Tourette's Syndrome and his insults were involuntary? In that case, you wouldn't fault him for his behavior. And why not? Because he couldn't help it. In other words, he didn't choose to do what he did. We measure human behavior by the choices people make, which is why we do not count behavior stemming from a brain disease. That's why our justice system has a concept called "not guilty by reason of insanity." If we exempt a crazy person from guilt simply because he doesn't know right from wrong and hence cannot choose between the two, we're implying that sane people do possess such an ability.
The concept of good and evil goes out the window if there's no free will. Sure, everyone agrees that some people are destructive, but as Hannibal Lecter reminds us in Thomas Harris's novel Silence of the Lambs, a storm is also destructive, and we do not refer to a storm as evil. Our society makes a strong distinction between who a person is and what that person does. We detest any system that places strong limitations on a person based on birth; that's why we have such antipathy toward the Indian caste system and doctrines of racial superiority. We hold that anyone, regardless of background, has the right to be judged by behavior, and not to be judged disfavorably until behaving disfavorably. Among other things, this belief forms a large part of the basis for rejecting preventative detention, the practice of locking someone up in order to prevent a crime. Our society would begin to look draconian if we truly followed the principle that free will doesn't exist. It would hardly lead to the "let's just enjoy life" philosophy that Vonnegut seems to favor.
But people who deny the concept of free will never seem to think through the consequences of their belief. Like those who claim that morality is purely subjective, they make a philosophical claim but don't live life as though they really believe what they're saying. In speaking against injustice throughout the world, Bertrand Russell certainly didn't act like he truly considered the difference between his own positions and those of, say, Hitler's, a mere matter of personal taste. And Vonnegut's portrayal of the horrors of war doesn't seem to stem from the position that the Nazis couldn't help the way they were. Undermining a basic principle of society is easy enough in the abstract, but few such people truly live by their words.