S.E. Hinton's The Outsiders can be interpreted to have a few different messages about violence. I think the first and most important message is that violence, especially between teens, is senseless and almost never ends well. This is illustrated through the deaths of Bob, Johnny, and Dally. In the first instance, Ponyboy was defending himself when he killed Bob, but because of his gang he was unable to see Bob as a person, only as a Soc. It is only later when Ponyboy begins to understand who Bob truly was as a human being. Johnny and Dally die on their own terms, but both of their deaths are a result of Ponyboy's initial misstep. At the end of the novel, it is clear that all of the characters have started to realize that violence creates more troule than good. In the story, these teenagers act like adults, and then realize that they are still kids who have committed very mature acts, and are challenged to face the repercussions.
Another message could be that, with determination, it is possible to escape a life of violence. At the novel's end, despite Ponyboy's involvement in the gang throughout his life, the reader is left to believe that he will go on to be successul in school, perhaps go to college, and escape his prior poverty and crime.