What is meant by this right is not that failing to impose punishment always wrongs them, but that they have the right to be treated as the kind of being who can be held responsible and punished.
Right (in philosophy)(as used in ethics and political philosophy)
A justified claim that others must respect or fulfill—like how you have the right to free speech means others shouldn't stop you from speaking your mind.
One more matter should be mentioned under the heading of the desert object: namely the idea put forward by some retributivists, that wrongdoers have a “right to be punished” such that not punishing them wrongs them (Hegel 1821; H. Morris 1968). It is important to be clear about what this right is. It would be ludicrous to hold that an executive wrongs a wrongdoer by showing her mercy and pardoning her. What is meant is that wrongdoers have the right to be treated as the kind of being who can be held responsible and punished, rather than as sick or dangerous beasts.