It's fun to be idealistic in a world of moral absolutes. I know because I'm a columnist. But when we start discussing history, things always seem to get complicated.

"The Daily Show's" Jon Stewart learned this recently when debating the Foundation for Defense of Democracies' president, Cliff May, about the harsh interrogation techniques administered during the George W. Bush administration.

When May asked Stewart whether he also considers Harry Truman to have been a war criminal for dropping atomic bombs on Hiroshima and Nagasaki, the host answered yes. A few days later, however, Stewart apologized for his blasphemy, saying Truman's decision was, in fact, "complicated."

Things were indeed complicated. They are always complicated.

That's the point.

Please, don't get me wrong. For numerous reasons, I'm ecstatic that the United States triumphed over the forces of jackbootery during World War II. But staking moral claims on old wars is a bad idea for either side of this debate.

In fact, if Barack Obama believes, as he recently stated, that the nation "lost its moral bearings" under his predecessor, he will have a hard time defending any presidency.

After all, if waterboarding is a war crime, the dropping of an atomic bomb on a few hundred thousand innocent civilians surely deserves some serious consideration for rebuke. At the very least, it's a fair topic for discussion.

Just as surely, Franklin Roosevelt's presiding over the destruction of Dresden, which caused 30,000-40,000 civilians to be incinerated, is at least as terrible as long-term sleep deprivation.

If Bush deserves war crime status for holding terror suspects in Guantanamo Bay (which Obama has yet to close), then we safely can say that FDR merits more of a historical lashing for the forced internment of 100,000 Japanese-Americans to "war relocation camps."

If Bush is a war criminal for denying terror suspects habeas corpus, then what is one to make of Abraham Lincoln, who suspended habeas corpus for all American citizens during the Civil War? Or of President Woodrow Wilson, who backed the Espionage Act, which forbade Americans from using "disloyal, profane, scurrilous, or abusive language" about the government?

Because, if we buy the argument that the ends never justify the means, we can't give presidents passes. If you argue that times and morality have evolved, that situations have changed, or that some causes are greater than others, then you're offering up distinctions, and you should accept some, as well.

The need to bomb Hiroshima and Nagasaki has been debated for decades. When President Bill Clinton backed the NATO bombing of Serbia -- at least 500 civilians were killed by NATO, according to Human Rights Watch -- he claimed that the bombing was necessary to "deter an even bloodier offensive against innocent civilians."

If that argument sounds familiar, it is because it is utilized all the time. Did the bombing of Serbia, Japan or Iraq save lives in the long run? Did the waterboarding of prisons save Americans from terror acts? I just wish a proponent would say, "We can't know for sure."

At this point, I can hear Jack Nicholson in "A Few Good Men" encapsulating the opinion of many: "I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the blanket of the very freedom I provide and then questions the manner in which I provide it. I would rather you just said 'thank you' and went on your way."

We shouldn't be on our way. In fact, history gives us a template to evaluate the complexities and morality of war.

And there are few absolutes.