This focuses on the "retribution/punishment" aspect of the penal system, but it's also important to remember that "deterrence" and "reform" are also important. Even if you feel people don't deserve to be punished for their crimes due to the crimes' inevitability, it's still important for repercussions to exist to create a society where it is less likely for people to commit those crimes (for fear of punishment), and where people who do commit crimes undergo a process that makes them less likely to do so in the future. (There are better ways than prison to reform people, of course, but not as many to deter people from committing crimes in the first place)