Should Robert E. Lee be considered a war criminal?

[Oski]

Inspired by the "Rank the Murderers" thread.

Some posters made the point that war = murder when it is not for the purposes of self-defense. I am not sure that it is that simple, anyway:

There comes a time in many wars that one side can clearly understand that it cannot win. In those cases, the losing side will attempt to position itself for a diplomatic resolution (or a surrender with some concessions). Once the "end game" is apparent, and the losing side can no longer improve its position, it can be argued that further figting serves no purpose and that further casualties is de facto murder.

After Gettysburg, Lee voiced the opinion that the South could no longer win a military victory. He also raised concerns that a political victory was unlikely. Nevertheless, he soldiered on.

After the Wilderness campaign, (despite the ghastly casualties suffered by the Union troops) Lee acknowledged that Grant was content to trade bodies as the Union was guaranteed to win the war of attrition.

As the Confederates were holed up in Peterburg Lee again acknowledged (as he witnessed his men starving to death) that he could not win. Nevertheless, Lee again chose to prolong the war by attempting a breakout to the West.

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Even without the benefit of history books, Lee was clearly able to understand that at some point after Gettysburg and the ensuring two years before surrender, that the war was a lost cause for the South.

Nevertheless, he chose to prolong the war at the expense of hundreds of thousands of civilan and military casualties, not to mention the destruction heaped on the South by Sherman, et al. as the Union was trying ot force surrender.

By most accounts, Lee was the one (and only one) person that had the ability to keep the Confederates fighting. Had he thrown down his arms, the War would have quickly ended. Not only did Lee fail to surrender, however, he urged his troops to keep fighting long past their breaking point.

At what point (if any) do Lee's actions amount to murder (assuming you accept the premise that there is a difference between casualties in a "justified" war and "murder" as we commonly understand it)?

Why was the Union so quick to canonize Lee after the War? I appreciate the fact that Lee and his family had a long history of service to the Union, and that mercy on him would speed up the healing process for the Union.

Nevertheless, aside from the practical reasons for showing mercy to Lee, why has history followed suit?

Long after the need to unify the nation has passed, why is Lee still considered an "American" hero as opposed to a war criminal?