Did the Nazi attempt to kill all the Jews warn mankind against ever trying again, or does it serve as a pilot project, to be improved upon next time? Must it even be an either-or thing? Maybe the Germans learned one thing, and the Islamists - the other? The one things that's certain is that mankind did not learn from the Holocaust to desist from genocide.
The Economist reports that a growing club of countries is sending its strongmen to Sri Lanka to learn how to destroy a terrorist threat. Inevitably they've got Israel on the list, but if you set that aside, it's an important but depressing development.
Many of us wish the trajectory of the human story was away from warfare and violence. Too many people, however, also believe this is reality, not merely a wish. Similar to the question about killing all the Jews, it may even be both: certainly in non-Balkan Europe, violence and warfare are utterly out of fashion - but not in the rest of the world, Not at all. This is probably not a blip, or an aberration, but a reflection of age-old human nature.