Will  at Ordinary Gentlemen writes:
I’m totally baffled by people who look to past atrocities for some sort of ethical guidance.
Well, quite so. One of the odd things about this is that it tends to make the atrocities even more central to the perception of the overall war effort than they might otherwise be. Instead of acknowledging them as wrongful excesses in an otherwise justified military campaign, which a reasonable person could easily do and leave it at that, the argument from war crimes has the strange effect of making the commission of war crimes seem absolutely essential to waging the war in question. While the defenders of these excesses may believe they are protecting the reputation of the government and the war it was fighting, they succeed mainly in affirming a double moral standard in judging wartime acts, thereby undermining the moral authority of the very cause they purport to be protecting against critics.
I would add that the recourse to past crimes to evade accountability for new crimes is a good argument in favor of enforcing strict accountability for crimes recently committed. If such crimes are permitted to go unpunished, their apologists will continue to work overtime to shape the debate in later years and decades in favor of the decisions leading up to those crimes, and the more time goes by the apologist will be able to fall back on one unassailable retort: “If this was a crime, why didn’t anyone in the government investigate and prosecute it as such?” Having warned against witch hunts and “criminalizing policy differences” in the beginning to intimidate the responsible institutions into inaction, the apologists will then remind the public that no charges were ever filed and no convictions were secured.
So, ironically, some of the defenders of the torture regime are making the best argument for the prosecution of past administration officials by their own invocations of past government illegalities. They are unwittingly reminding us that crimes unpunished today can easily become tomorrow’s conventionally accepted “correct” decisions. Every usurpation or instance of lawbreaking that is not challenged and reversed creates a precedent for the next round of usurpation and lawbreaking, and the fact that there is a non-trivial number of people in America who think that the illegal acts of Lincoln, FDR, Truman or others should have some mitigating effect on how we treat illegal acts under a more recent administration is one of the best reasons why crimes committed during the last administration must be investigated and lawbreakers must be prosecuted. Had many past administrations been scrutinized and their crimes investigated and punished, it is less likely that we would have to cope with an executive branch that acts as if it is above the law and which seems to be able to to break the law with impunity. If we fail to hold past administration officials accountable, we not only make a joke out of the rule of law, but we ensure that no legal or institutional constraints will prevent a future administration from committing similar wrongdoing in a time of crisis.