"Retribution" is sometimes confused with "vengeance." And admittedly, the distinction can be subtle. But it is not wrong to demand that an aggrieved party be accorded some satisfaction of his grievance. In fact, it is the ultimate balancing of the cosmic scales. When one turns over the authority for such satisfaction to a dispassionate third party that observes a strict due process in its administration, then it can be said that to the degree humanly possible, blood lust has been removed and the result distilled down to its judicial value.
That is what capital punishment does. It metes out retribution according the accused every protection under the law. It dispenses justice without anger or hatred, but purely in the spirit of balance.
It is interesting to note that Justice is depicted as a blindfolded woman with a balance (not a scale) in one hand and an unsheathed sword in the other. The symbolism is that once the balance has served its purpose, it's the sword's turn.
Nicely put.