I see four angles on the sentence: Justice, Revenge, Politics and Deterrence.

The DP addresses revenge and arguably justice. IMO, there can be no justice served by any type of sentence in this case. What the DP doesn't achieve is deterrence. The DP will not deter people who are not afraid to die and glorify a death for their cause. It will only motivate them. Judging from the descriptions above, life imprisonment in a hell hole is more likely to be a deterrent.

Politically, you can't win either way.

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