Incapacitation and just deserts as motives for punishment

What motivates a person's desire to punish actors who commit intentional, counternormative harms? Two possible answers are a just deserts motive or a desire to incarcerate the actor so that he cannot be a further danger to society. Research participants in two experiments assigned punishments to actors whose offenses were varied with respect to the moral seriousness of the offense and the likelihood that the perpetrator would commit similar future offenses. Respondents increased the punishment as the seriousness of the offense increased, but their sentences were not affected by variations in the likelihood of committing future offenses, suggesting that just deserts was the primary sentencing motive. Only in a case in which a brain tumor was identified as the cause of an actor's violent action, a case that does not fit the standard prototype of a crime intentionally committed, did respondents show a desire to incarcerate the actor in order to prevent future harms rather than assigning a just deserts based punishment.