Seeing that retribution is a moral concept, a definition of it is why it is moral. If I asked you why you thought rehabilitation was moral, a defintion of rehabilitation would suffice.
Let's put it in another way; why do you think the government is justified in carrying out acts of retribution?
Yes. It is not legal, but it is moral.

Ok, what if we glaze the Middle East due to 9/11. That's an act of retribution as well. So is it then moral?
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