Culpability is a moral consideration related to justice. It concerns how we respond to guilt and innocence. As with need and merit, culpability concerns equitable treatment, rather than equal treatment. That is, we give extra consideration to those who have committed crimes or harmed others.
What this consideration amounts to is quite simple and intuitive: we believe that -- if a crime or harm is committed -- all and only those who are guilty of committing that crime should be punished, condemned, or in some sense be held responsible for it. Those who are innocent, who did not commit the crime, should not be punished or held responsible in any way.
Culpability is sort of the flip side of merit. You could say it's merit versus demerit. In the same way that we praise and reward people who do good -- as we do when responding to merit -- we also demand that those who do bad be held responsible and punished. And, of course, we also insist that those who have done nothing wrong have nothing wrong done to them.
This leaves a lot of subsidiary issues to consider, such as whether and how the guilty should be treated. The Civil Debate Page goes into some of these issues in the sections on defiance and punishment.
Culpability and Other Considerations
Frequently, we have to weigh the moral desire to punish the guilty (and only the guilty) against other moral considerations.
For instance, we often think that it's OK for the police to hold a person in jail prior to trial, effectively punishing them before they've actually been found guilty of any crime. Criminal suspects are typically remanded in custody if they might pose a risk to others: If you're pretty sure you've captured a serial killer, it seems unreasonable to allow them to roam free -- potentially killing more innocents -- until they've been convicted of their previous murders.
(Generally, though, we demand that there be substantial evidence of guilt before suspects are remanded, which is another bow to the drive to leave the innocent unpunished. Hence the burden of proof requirements in the justice system, and the admonition that we treat people as "innocent until proven guilty".)
Similarly, we often face a quandry when it comes to handling sex offenders. It is believed that they are very likely to commit such crimes again. In order to prevent them from doing so, it is often suggested that significant restrictions should be put on them even after they have served out their sentence. On the one hand, this seems like a good idea, if it really does serve to prevent them from committing further sex crimes. On the other hand, however, it also seems like it amounts to punishing them for crimes that they have not (yet?) committed, future crimes for which they are (so far?) innocent. And this runs counter to our moral desire to only punish the innocent.
Culpability Versus Culpability
And, of course, we often have to prioritize between different levels of culpability.
To use yet another example from the criminal justice system, sometimes a person who is guilty of a crime is granted immunity from prosecution (or is allowed to plead guilty to a lesser crime) in exchange for testimony that will convict someone who is guilty of greater crimes. These plea deals are often considered justified -- if somewhat unpalatable -- since we are giving up on defying and punishing a lesser offense in order to secure the punishment of a more serious offense.
Likewise, another reason for remanding suspects in custody is to make sure they don't flee and evade trial, depriving us of the process that assigns guilt. We're willing to risk unjustly detaining an innocent person in order to make sure a guilty person doesn't flee the justice system altogether.
And, just like -- in the name of compassion -- we give more attention to a person in greater need than the one in lesser need, we give more attention to the person guilty of committing a greater crime or harm than one committing a lesser crime. If a police officer sees one person making a littering violation and another person committing a murder -- and he can only chase one of them -- of course he should go after the murderer.
So, the role culpability plays in our moral reasoning can be quite complicated. But the basic moral intuition itself -- defy the guilty, leave the innocent alone -- is fairly straightforward.