Many who reject the notion of free will think that punishing people for crimes makes no sense. they think that instead of punishing criminals, we should

The correct answer is try to modify their behavior

Those who oppose the idea of free will believe that humans are not personally responsible for their behavior, life outcomes and actions. Those opposed to free will would believe that punishing people for crimes is pointless, and instead of doing so, their behavior should be modified. They believe that the latter is more effective because by modifying someone's behavior they will be less likely to commit crimes and become repeat offenders.